How can Bitcoin protect itself from a "dumb majority soft fork"? Let's say a majority of miners change to using software that prohibits timelocks. This would be a softfork, so the blockchain would still look valid to nodes using the previous software, however nodes that mine blocks with a timehash would be orphaned from the network by the mining majority and outpace any chain containing timelocks. No chain that contains timelocks could grow, and existing nodes would treat the chain with new rules as the one true chain.

How would the users/miners that want to keep the use of timelocks be able to recover in this situation?
If the users who want to keep the use of timelocks do not constitute even a significant minority of users, they're simply out of luck. There's no mechanism for a minority to force the majority to tolerate rules the majority doesn't want.

Assuming the users who want to keep the user of timelocks are significant, they first communicate their intention to miners to take their business elsewhere. If they leave, they will take a good sized chunk of the ecosystem with them, reducing the value of the remaining system.

Even if they're not a majority, most users will not want even a significant minority to leave. So they can put additional pressure on the miners. The ultimate threat if the miners don't do what an economic majority of users want is that users can change the hashing algorithm changing the miners' precious ASICs into expensive space heaters. Or, to be more precise, changing them into expensive space heaters a bit faster. The miners definitely don't want that.