Will being away for 3 weeks affect my playing much when I get back? Like will I regress in ability or anything?
maybe a little, but it won't be a noticeable decrease
YOU WON'T REMEMBER HOW TO PLAY!! nah you'll be fine, you might be a bit rusty but, you'll get through it quickly
Yeah you'll be noticeably sloppier and it will probably take you a while to get your right and left hands in full synchronization again. I will be doing a 3 month campaign of mineral exploration work coming December, pretty much might forget how to play the guitar :s
Your hands won't be used to playing, and your callouses will most likely go away but no detrimental effects.