Power outages aren't common enough here that this is a big concern. And since the network is likely to be down, there is likely zero point in keeping your server online. (Your services can survive a reboot cycle right?)

If the services are required to be online, it's likely you'd want your network online as well so you'll need a battery backup for your router. So you run the Raspberry Pi on the same battery backup you have your router on.

I believe running a MacBook as an always on server will pretty rapidly destroy the battery anyway.

Macbook appears to be pretty intelligent about it's battery. My 2016 is still over 90% healthy and regularly gets over 5 hours on a single charge (load dependent of course). It's pretty much on 24/7.

The issue is that the battery never gets a chance to discharge if you’re using it as a server. Unless you’re unplugging it and monitoring the battery life and plugging it back in every day.

Hmm, most of my work laptops never get used unplugged and I've never had issues.

It might be fun to implement some sort of service that checks battery life once per day and turns off a smart plug (which the Macbook power adapter is plugged into) and lets the Macbook drain once per day before turning it back on, though.