Many people mine Monero in a pool. Monero has recently changed its proof of work, and it is about to do so again. There may be more changes to its proof of work in the future.
When miners update their mining software, they will presumably do it in advance of the proof of work change, meaning the mining software should be able to use the existing proof of work or the new proof of work. Miners don't have a blockchain, of course, so the mining software itself doesn't know which algorithm to use.
Pools have a blockchain, of course, so they will know what type of proof of work is needed. When it is time to change to the next proof of work, will pools automatically request the new proof of work from its miners? In other words, if miners and pool operators upgrade in advance of the proof of work change, will the network seamlessly switch from one algorithm to the next?