Frankly, Istredd isn't considering that at all. This is where his blindness outside of his goal can be a real problem. Luckily he is going with people who can counter his flaws, so Stephen has handled things with Ambrose and will be the balanced one of the group. Istredd's entire focus is on the Singularity and what may happen there. He has faith that they won't end up dead, mostly because the Singularity will be at its weakest.

Most of the mages at home have telepathic links of some kind, especially when working together. They talked all the time at school that way, and also trained for in-combat reasons. It can't go halfway across a continent, but within a certain distance, it is clear as a bell. So there is an unknown if it would work from the Singularity, but they could at least try. And he can probably push it and send a message as far as possible.

"Alright, we'll have to go back to the real world. If it works, we won't have to worry about people listening in."

If they were using common telepathy it is possible Thorne could press, but Istredd is very strong, his defenses are difficult to get around and he would sense it. But this kind of bond is different. He leaves the Horizon, waiting in the room, still a little apprehensive.