A place might reasonably be deleted or have information removed if
- it has been marked as closed
- it has been confirmed closed (in case a competitor just comes along and says 'it's closed')
- it is not temporarily closed (moving, changing hands or refurbishment)
- it has no connection to another place (part of a chain)
- some cooling period of time has passed
So even if a branch of a chain closes, the relevance of these ageing reviews to people visiting another branch will decrease over time (say 6 months) until such time as they might no longer be of interest.
How you manage merging the reviews of multi-branch chains is up to you, but if you are reviewing branches individually, I don't think you need to do anything special when one branch closes. Those reviews are not suddenly of any more significance to any other branch. If you follow the cooling down idea, then the closed branch will fade out of use naturally and no one will notice its removal 6 months later.
The cooling period can be short for a unique place and long for a branch of a chain.
It can be multiplied by a popularity factor. If it had many reviews, extend the cooling period. If it had very few reviews, reduce the cooling period. This will also have SEO benefits because you will receive hits to a popular page and it would be a shame to lose those just because you removed that place within days of it shutting down.