Talk to your plumber about a sewer check valve. Sewage backups are rare, but depending on the layout of your plumbing it might be a reasonable price for the peace of mind it offers. This actually happened to me. Thankfully my sewage line has an open vent pipe in the yard (I don’t think this is up to code anymore, but my house is old), and rather then enter the house the sewage simply spewed from the pipe until the town fixed the sewage main. A sewage puddle in the yard was bad but had it been in the house it would have been 100 times worse.