segwit address coins can be spent by anyone if segwit is no longer running on the network.
Well, that is kind of true. And kind of not. And I'm a Bitcoin Cash advocate, so keep that in mind.
First off, the only segwit transactions that are subject to the anyonecanspend issue are ones not already mined into a block. So if the miners wanted to to claim the value in those newly-anyonecanspend transactions, they would need to roll back the blockchain to release those transactions. Game theory suggests this is unlikely to happen.
Secondly, once those transactions become anyonecanspend again, while it is true that anyone can claim the value, those doing the claiming need to somehow get their claim mined into a block. As miners are able to mine any transactions they care to, and as miners are also able to claim these anyonecanspend transactions, this essentially makes these anyminercanspend transactions. The miners will ignore any competing modified transactions in preference to their own.
Of course, this latter fact is what makes my first observation above less than absolute. As more segwit/anyonecanspend transactions get bound up in the blockchain, the incentive for miners to collude to roll back the chain increases. With each and every segwit transaction.
It baffles me why the Bitcoin Segwit Core advocates -- who claim to distrust the miners so vociferously -- are able to look away from the trust they need to have in miners due to this issue.