Obviously, but this an answer to a question that wasn't asked and I think everyone understands you can MANUALLY cancel an offer. That's the PROBLEM, not the solution.
Plus, it's hardly an elegant or seller-friendly process to get rid of old offers, especially for those with large portfolios and pages of open negotiations. It's like giving a hammer to a guy with an ant infestation and calling it a day. "Just hit 'em with the hammer'.
There are also other points to consider:
1) This "forever offer" format is not communicated anywhere in the negotiation system and I would bet few Spaceship users even realize that if each and every offer is not manually cancelled, then they will remain active forever.
2) To my knowledge, no major domain marketplace uses "forever offers" and all have expiry dates, with some offering flexibility to choose the number of days.
3) Sellers with massive domain portfolios that generate lots of offers each day are going to have a manual processing nightmare, deciding the timeline on each and every one of their offers and setting alerts on when to cancel them, and that's it they even realize that Spaceship uses "forever offers".
The last thing I need is to go back to the 1980's and have to manually keep track of an entire marketplace system in 2026. It's just more work for me, and something that an online system should be taking care of.
People complain about cached, lower-priced BINs being purchased, so I can say with certainty that this "forever offer" system will inevitably result in old, forgotten offers being exhumed by industrious buyers, at a discount price that was only intended for that point in time. Better not forget about those, or they'll be sitting on your account forever just waiting to be activated.