Opeth isn't going to break up for 5-10 years at least, barring any Cliff Burton-type accidents (god forbid).
Honestly I'm not sure where they will go, if anywhere, content-wise. Many will probably disagree with me, but from Still Life on I think they've largely stopped evolving or changing in any real substantive way. The first four albums - Orchid, Morningrise, My Arms, Your Hearse, Still Life - are all quite different from one another and you can see both the change and the continuity in each.
To me, there was very little if any evolution of their sound on Blackwater Park, Damnation/Deliverance, and the Grand Conjuration, with the possible exception of the interesting rhythm part in "Wreath" off of Deliverance. What I mean specifically is this:
- after the departure of their bassist DeFarfella the interesting bass work (see Orchid and Morningrise) disappeared. Then again, the song styles changed a lot with MAYH and there wasn't as much room for the same kind of bass stuff.
- from Still Life onward Opeth adopted traditional song structures: chorus, bridge, etc. This I think has been a big reason why their last four albums sound a lot alike to one another. Up until Still Life, every melodic line and amazing riff was heard ONCE, which at first for me was frustrating but I came to appreciate it later on as I realized how hard it must be to write great songs that don't repeat.
- many of the albums and songs have the same mood/feeling. If you listen to Morninrise and Orchid, many of the songs have a bright, almost upbeat and youthful quality to them which made the music quite a bit more dynamic than it is now.
So I guess I don't know what Opeth will bring us in the future. I hope they re-integrate some of the elements from their first few releases into their new stuff or incorporate things that I can't really imagine. I understand that Opeth has moved on quite a bit and grown a lot as musicians since their first couple albums but I do think there are elements in their older, less mature work that would help them create better music today.