I think the best thing to do (except from discussing this with your
ortho and take his/hers advice of course), would be not to change to a new tray but wear the old one for an extra 4 days. And try wearing it as much as possible! There surely won't be any problems wearing them at night? And I don't really see a problem with the eating either, but you can at least wear them until you eat and if you for some reason can't brush right afterwards you can do it whenever you get the chance. I would imagine that you have to visit a bathroom a couple of times every day anyway for other reasons..
I definitely think it would be better to wear them at night and some hours during the day than not at all for 4 days straight. If you wear your current aligner you won't have to be so afraid of losing it either - I mean, since you think you can cope without it, it wouldn't be a tragedy if you brought the tray and lost it after 2 days.. it's still better than going 4 days without!