After the day of the merge, what will happen to the contracts that haven’t been updated since a long time (inclduing e.g. updates to work with new metamask, much less to work with 2.0)? Will they stop working?

Some contracts haven't been updated in a looooong time. Some websites dont even work with the "new" metamask. What will happen to them after the 2.0 merge? will they still work? will you need to do some tweaking to interact with them? will they be part of the 'legacy' ethereum that will still work?