continue to tag them, plot with them lightly, etc. let them know they are still wanted and you do want to play with them. but don't engage in any plots or deeper cr developments that might be dependent on them. this lets them continue to enjoy things at their own pace but doesn't potentially put you out (which would make them fret/feel guilty even more).

tl;dr be cool about it. don't over think what they're doing, just focus on what you need to do to keep having fun. either they will come around or they won't. rp is not a big deal, even if their brain is fretting and making it one or unfortunate external circumstances are making rp difficult for them in the interim.