How likely is a 25U to be sent to pathfinder school?

Damn unlikely, because 1- your unit will have to pay for it, 2- what justification can you make to the unit to allow it.

Probably not very likely. Especially as a Guardsman. But, you never know until you request a course seat from your unit/state.

Not likely but the time to ask is at the end of a fiscal year where they need to spend the money or lose it. They may just say "got ahead and send him". Sometimes request for going to schools, timing is everything.