These people have dual citizenship and their actions have demonstrated their allegiance is not to Canada. Canada owes them nothing.
Of course many who went to fight for ISIS were born in Canada, so they can be jailed forever IMO.
Here's the oath of citizenship:
I swear (or affirm) that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth II, Queen of Canada, Her Heirs and Successors, and that I will faithfully observe the laws of Canada and fulfil my duties as a Canadian citizen.
If you revoke your allegiance to the Queen of Canada and go off to fight against her, you've fundamentally broken your oath, are a traitor, and it would be fair if they lost their citizenship. Otherwise, just throw them in jail for the rest of their lives.
Khadr is a murderer, not to mentioned a traitor and a terrorist, and yet is walking the streets, which is interesting.