I've considered this before, but also been proudly self sufficient. More than one cyclist has benefited from a roadside wheel rebuild (with parts) I have supplied for free, in the same way I have benefited from others supplying me assistance.
I was actually thinking about this again the other day but then realised anything within cycling distance is also within walking distance, albeit a bit slower. In an absolute emergency 999 will get you the ambulance to look for the missing limb, otherwise it's time to phone a friend or walk to a lodging of reputable repute and request a room for the night. On the last big ride I had a pre-planned room booked, but didn't spend much time in the bed due to rebuilding the bike after stupidly using a cycle path and managing to limp the last few miles there.
For the people who have signed up and it's worked, I'm glad it has worked for you.