I think any program would want to know ASAP if you were not planning on renewing your contract. How they would react to it--I don't know. I would hope most would be understanding about it. IT might also help your case if your program has an "overabundance" of 1st & 2nd years. Its residents in those 2 years that provide the most call coverage. If someone in my program wanted off but there were enough residents to provide coverage, my program would probably be much more likely to allow for the time off.
As far as I know, if you complete your 1st year-you earned it. No one can take that away from you so long as you remain in the program. If you enter back into your program you should be a PGY-2. However the program may cut you loose & not let you back in. In which case you'd have to reapply to residency, and some programs may only offer to take you as a PGY-1, and a few may allow you enter as a PGY-2 (difficult though possible).
Also, the GME at your program can inform you of your rights in this manner. Your personal situation may warrant that the the program must allow you time off if your situation justifies this. However your program's rules may also possibly force them to not allow you the time off-forcing you to either not take the time off or resigning. There usually are specific policies concerning this at the GME. Know your rights & the rules, and see if your situation can be accommodated to your satisfaction.