Every country I have dealt with has been flexible with regard to the need for a zarpe. They all have known, for example, that the USA doesn't routinely issue zarpes, so not having one has never been an issue.
On the other hand if you are coming from a country where clearing out is a legal
requirement and you don't have one, they will certainly be asking you "Why not?" and if you don't have a good answer, expect more considerably more pointed questions.
For countries that do routinely issue zarpes, but where they are not required to leave (e.g., Bahamas) I always get one if I am going on to anyplace other than the USA. If I am leaving the USA, I don't bother with the hassle of getting one even though it is theoretically possible.
For us, getting clearance documents out of TCI has never been a problem.