As the Islamic State continues its mission to turn Syria, Iraq and the wider Middle East into a caliphate that is as radical as it is brutal, droves of Christians are making the heartbreaking decision to leave their ancestral homelands, knowing that they may never return.

ISIS militants have been merciless to Christians and others who fall into their hands. In February, the world was shocked when a video emerged showed 21 Egyptian Copts being lined up and executed by ISIS militants in Libya. This was followed soon after by the execution of Ethiopian Christians. Churches have been the target of fatal attacks, and earlier this month the Fides Catholic news agency reported that ISIS was turning one of the largest churches in Mosul into a mosque. Tens of thousands have been displaced, surviving on patchy humanitarian assistance.

Even before the grim onslaught of ISIS, many Christians in Iraq and Syria, ground down by years of conflict and hardship, had chosen to pack up and leave. However, the barbarity of ISIS has only served to accelerate the departure of Christians from the region.

One Christian man named only as Ammar told the Christian Broadcasting Network last month of how he and his family got out of Qaraqosh, Iraq, when the bells tolled in the middle of the night to warn that ISIS was on its way. 

"Very strange [that] bells ring at this time," Ammar recalled. "So the loudspeakers belong to [the] church [and] the loudspeakers call out, 'All of you, go out from Quaraqosh. ISIS is coming and there is no one to protect you.' So I take my family, my wife, my children and go."

Another refugee named only as Raged told the broadcaster: "They don't want any Christians to live in Iraq. They want to kill them all or have them leave or become a Muslim."

At a panel this month hosted by the US-based think tank, the Council on Foreign Relations, experts discussed the prospects for the survival of Christians and other minorities in the Middle East. The panellists concluded that their utter extinction is not out of the question if things continue as they are.

Panellist Andrew Doran, a special advisor to the US-based group, In Defense of Christians, said it was "certainly within the realm of possibility". 

He warned that if the Syrian capital of Damascus falls, huge numbers of people will be forced to flee, with the Christians most likely to make their way to Lebanon.

But it would not be an easy exit, he said, and there would also be potential dangers for Lebanon.

"There would be mass slaughter along the way if this were to happen, because if Damascus would fall, you could reasonably foresee that Aleppo and Hams would fall, and Lebanon would become suddenly very vulnerable," he said.

He went on to state, "It is entirely possible that the very worst for Middle East Christianity lay ahead... in the foreseeable future."

With the prospects for Christians remaining in Iraq and Syria so bleak, some voices are calling on the West to increase its efforts towards a coordinated resettlement.

Writing in the National Review in June, Nina Shea said it was time for the international community to shift its response from a largescale aid effort focused on helping exiled Christians to exist, to a full blown strategy that would provide them with sanctuary.

"The only achievable strategy under the current circumstances is to prepare for an orderly resettlement of these Christians (and Yazidis) in the West," she wrote.

"It is a bitter development for the Church and for them, being discarded after 2,000 years of history, through no fault of their own. But it is the most humane of the alternatives. Otherwise they face indigence and exile or, worse, slaughter at the hands of jihadists.

"Widows, orphans, and the most deeply traumatized should be given priority. Some vow to stay and fight, and they should be allowed to do so. Each family should be able to make its own decision about whether to go or to stay."

While Western powers dither over how to fight ISIS, one Jewish politician in Britain, Lord Weidenfeld, made the surprising revelation this month that he was overseeing his own rescue mission to bring trapped Christians out of Syria and Iraq.

He is funding a resettlement project for some 2,000 Christians from Syria and Iraq, and last week saw the arrival of 150 in Poland after being transported on a privately chartered plane.

Explaining the unusual move, he said he had a "debt to repay" after Christians helped him as a child to escape the Nazis in Austria.

He is not the only one sensing that Britain should do more to help Iraqis fleeing ISIS. The Bishop of Coventry, the Right Reverend Christopher Cocksworth, and the General Bishop of the Coptic Orthodox Church in Britain, Bishop Angaelos, have publicly urged the British government to open its doors to those seeking to escape the Islamic State.

Speaking to the Sunday Express several weeks back, Bishop Cocksworth went as far as to say that Christians should be given priority.

"Christians made up a quarter of the Middle East's population 100 years ago, now they are less than five per cent. This is where the EU needs to act. There needs to be some sort of calibration that places these Christians at the top of the list," he said. 

"The most necessary thing is to prioritise the most vulnerable. If Christians are the most vulnerable - and there is no doubt about it that in many cases they are - then there is a case for it.

"This is a severe humanitarian crisis that puts Christians on the front line, and it is irresponsible to ignore religious affiliation.

"There is a need for the Foreign Office and all departments including Dfid to recalibrate resources for this crisis in which religion is seen as persecution used as a weapon of war."

He is not alone in feeling that Christians in particular are having a tough time. The World Evangelical Alliance's Religious Liberty Commission said Christians were "one of the primary civilian targets" of the Islamic State and that one of its goals is to eradicate minorities from the territories it controls.

Certainly, the physical conditions for those who have stayed behind are extremely difficult. Open Doors USA puts the number of Christians in northern Iraq and Syria in need of emergency food support at 300,000. The World Evangelical Alliance says that out of the 1.1 million Christians who were living in Syria before 2011, some 700,000 have left the country.

Chaldean Catholic Patriarch Louis Sako of Baghdad recently described the emotional toll that the threat of ISIS is having.

"We feel forgotten and isolated. We sometimes wonder, if they kill us all, what would be the reaction of Christians in the West? Would they do something then?" he said. 

In response to this plea, the World Evangelical Alliance is asking the international community to do more to protect displaced Christians from further attacks and provide for their basic needs.

"Let's hope, pray and make our best efforts so that Christians in the Middle East would not feel forgotten in their most difficult time," the organisation said.