How do you read that at all? I fail to see why they would stop. It's not "logical" that PT would die, at all.
To begin with, I don't feel like SW is as dependent on PT as DG is on PoS.
Not saying that it's negative, but meanwhile Daniel has mostly focused on PoS and explored what he wants to explore there, SW has explored several different styles in several projects, and I don't think people see SW as "that frontman in PT", seeing how many other things he has done as well. (no diss on Daniel really)
As much as some people on the net can argue that PT is 100% Steven Wilson, he would probably say the opposite himself, and I find it hard to believe that he would replace friends since 20 years (Colin and Richard), maybe if one left, but if both dropped out like the scenario in PoS, then half of the magic in studio would be lost.
There wouldn't be the same people to discuss ideas with, and I don't think SW would be AS into it, because after all, I think it increases the joy if you play and perform with people you really like, and have known for a while.
We also have the perspective that SW would probably do very well without PT as well. He has established himself very well as a musician, apart from the music he has made, the "collaborations"/mixing and producing, the latter part alone probably gives him some solid income.
I don't think DG has the same situation, obviously a lot of doors would open since he's an amazing musician and all of that, but he has his family at home, I don't think he does quite as well as SW financially (I'm basing this on what I've seen in documentaries and interviews and such, might have changed), add to the fact that PoS has been his money-source for the last 14-15 years, and other small factors.