Subject to - what happens to the seller?

[Henrik Frank]

"Subject to" deals sound like the holy grail. The seller gets to sell (and likely at a decent price) and I pick up a house without spending (much) money. If it can be rented to cover and eventually be sold at a profit, all are happy.

However, I was wondering what happens to the seller in the meantime? He would obviously still have the mortgage on his credit - I assume this would significantly lower his possibility of buying a new place and maybe even his ability to rent a home?

Also, is the end date of the contract always a fixed date (e.g. we will sell the house exactly 3 years from now) or is it more of an option to sell anytime before the expiration? (If the latter, I assume longer contracts would be better...)

Thanks!