Hello!
I think I may have to travel for a prolonged time, probably a month or more, starting this summer, not sure when exactly.

The question is, what I will lose if season ends and I wont be able to finish it properly being away from PC for months?

I already finished all season tasks, now just fishing and waiting for early grad they removed for unclear reasons.

Thanks in advance.

Early graduation is always enabled a month or so after season begins.

No losses.  When season ends Tuvala gear will be automatically converted, and you'll get the rest of the season end packages.