I never really hear any feedback on this arrangement from anyone though, the little feedback I have got so far suggests people appreciate that multiple parties have differing levels of control over the forum. The forum is not my top priority since I focus more on bitcoin.org, so if anyone has the feeling they would prefer theymos being fully responsible for bitcointalk.org, it would be good to at least hear that opinion expressed.
I'll echo the sentiment that things are working well for the time being. It seems like you and theymos have an amicable arrangement, and from what's been said in the past I don't see that changing any time soon. Cheers, and thanks for weighing in on the subject.
However, for the very long term, assuming Bitcoin and this forum will last, there should be either a permanent solution or at least an order of succession.
You bring up a very valid point. At some point it may behoove those involved to consider how to protect the forum and ensure it's availability for future generations. I don't know how old theymos and Cøbra are, or how often they go sky diving, or buy black-market vape products, but it's definitely worth having the discussion at some point.
The domain name, physical servers, and database could be transitioned into a trust, or a corporate structure with a board of directors. If I'm not mistaken the Bitcointalk.org entity exists within the United States, another option could be a Limited Liability Partnership. I'm no lawyer, so I don't know which of these business entities would best suit the longevity of the forum while keeping it's value in the hands of those who currently "own" it.