If you lose pro, then but it again about a week later, will your stats still be there as they were before? Or will they bee gone?
Yes, your stats will remain.
As long as it is linked to the same Google/Facebook/IFC account, your stats will remain.
This isn’t fully true - as long as you’re using the same App Store/Google Play account, you’ll be able to recover your accounts and stats :)
Well, yes. Except for maybe time-specific requirements (landings, etc.). So you may have a lower grade.