I've lost track of how loans between Prem clubs work? Is that not an option. Would give Brighton chance to see if he could cut the mustard, I mean if he can hack it at a newly promoted team who'll probably be under the cosh most games he can make it anywhere.
Nothing in it for Brighton.
If they sell their keeper, they need a replacement, which is what they'll see Rushworth as. I'd imagine if they want to keep him, and keep him happy, they need some guarantees of first team football for him next year.
Also, I wouldn't want a player on a buy-back. Sell-on fees, yes, but a buy-back is not much more than a glorified loan.