I would get a nice clean happy chain before starting and then continue using a good wax lube throughout and wipe as needed. Since wax lube generally keeps my chain cleaner I really don't deep clean them much and sometimes just give a light wipe with a rag. I personally use Finish Line Ceramic Wax Lube and love the stuff but I don't give two doo-doos about the lube and don't feel the need to see people argue.

If things did get really muddy I would likely do my best to get mud of the derailleurs and such and maybe rinse the chain with some water, wipe and relube. If really bad and near a bike shop or auto shop I might try and use the parts washer but knowing me I probably wouldn't unless it wouldn't shift or shift well enough.

If I knew I was gone for a really long tour I might find a shop at a certain mileage (beforehand) special order a chain I needed (or make sure they had it) and then gone in and replaced it or if I was in a foreign country like Canadia where they don't speak 'Merican (relax and laugh) I might just carry an extra chain with me. Or I might reach out to the shop and try and borrow some stuff or let them do a little DT clean.