Has anyone travelled from Bayeau to Paris by bus?
Before you panic, know that on a strike day not ALL trains are cancelled -- we had two train rides scheduled for strike days during our current trip, one was cancelled but we were able to switch to another an hour later, and the second ran as scheduled although the train before and the one after were cancelled and people were rebooking onto the available trains.
I had train tickets from Paris to Rouen on a strike day. I knew about it weeks in advance so I bought a FlixBus ticket just in case. I didn't need it, but I've heard that the buses are just fine, and I was totally prepared to do it.
What you need to do is on the night before the scheduled train, check the SNCF schedule on line and see which trains are running. There will be trains running, just far fewer. If your train is cancelled, you can take any train that IS running, either earlier or later on that same day. So, you'll get where you need to go. You may have to stand.
We lucked out and our scheduled train was one of the few running.