Interesting experience as a data point, definitely a YMMV:

Had AF Amex for about 15 months, upgraded to Surpass for the bonus in 12/12, posted 1/12. Downgraded to no AF in summer 2013 and got partial AF refund.

Had a bunch of HH stays coming up in late 2013 so upgraded in mid 10/13 and charged a partial AF again in 12/13. In 1/14 was pleasantly surprised to see a 50k bonus pop up in my account (just happened to spend >3k after upgrading, didn't expect bonus). Can't complain, particularly with Amex bumping HH spending up to 18 pts/$ for surpass over that period as well as giving gold status automatically.

Also was told status would not be rescinded if I downgraded again; I spent 20k in 2013 so would have gotten gold with free card, but called to make sure I wouldn't fall into a weird trap with having a surpass in early 2014 and then downgrading.