I've been in IT all my life, starting in the mid 80's. Got an extensive home lab and host pretty much everything you tend to use as SAAS these days at home too. Home mail, cloud, web based office suite, etc.
But for the "what if your ISP goes down", well, then I switch to my neighbors ISP XD.
There's dozens of ISPs of various sizes where I live and there's neighbors representing 8 of these ISPs. I have access to all their networks (most of them gave access).
So if my ISP goes down, I switch to another one.
That said, I haven't had an outage longer than 30 minutes in 5 years and the average time between shorter outages (quick resets to minutes long) happen 1ce a year or so.
There are some announced outages, usually once per quarter, for network upgrades and system maintenance. But generally, my ISP has a 99,99% uptime.