Moving a server from Ubuntu to Debian doesn't seem a very arduous task? I've got a box in a rack that came from the factory with Ubuntu installed, but there are Debian addresses in /etc/apt/sources.list.d
Besides isn't that pretty much the exemplar of FUD?
But it is still a task, isn't it? So, now you move to Ubuntu, then if things get south, you move to Debian. Or, you could move to Debian or other less risky distribution now and likely save some time and energy.
On the other hand, maybe Ubuntu is providing something special that Debian can't do - then it may make sense to go with Ubuntu and maybe even swallow Microsoft's fishing hook if it comes.
Besides isn't that pretty much the exemplar of FUD?