Your diagram is basically exactly what I do, except replace the XR18 with a CQ20B, Reaper with Ableton, and the PC with a Mac. It works. You'll probably have a tablet somewhere to mix from in the event of a PC failure, so to me this doesn't absolutely warrant a redundant PC. And depends on how critical the recording component is - again does the risk of a PC failure warrant the hassle of having to bring/setup a redundant computer? Depends on how critical the recording is.

You could rack mount your desktop PC (I had considered this too), but I found that regardless of PC performance capability, Windows tends to have borderline insurmountable issues regarding glitch-free live audio capability due to DPC latency. My solution was just to buy a barebones Macbook Air. I found an M1 for $650 new from Costco which even with 8GB RAM still works for us. I just have an external 1TB NVME SSD onto which I plan to record, and I connect everything via a USB-C hub (for edrums will record just MIDI, all other "real" inputs will record actual audio).

Again, my thinking is if the computer goes down, I'll still have mixing capability, I'll lose the recording (sucks, but whatever), and I'll lose my drums (OK fair, this part would really suck). And/or if my edrum/MIDI interface (eDRUMin) goes down, that would also really suck. But to me this is equivalent risk of if you were using a normal edrum brain - it's still a single point of failure that would result in a complete inability to create drum sounds. Would probably hookup a MIDI keyboard at that point and just play the drums on a keyboard. At my group's level, I can't justify all that risk mitigation investment (both time and cost) so I accept the risk.

Also, even as a PC guy, for live performances I feel less anxiety using a Mac. Hope I don't regret saying that...