four days away, DS 21mths - what will happen?

[AndMiffyWentToSleep]

I've got to go away for four days - at the moment 21mo DS is only fed at bedtime (and also sometimes at naptime at the weekend).

Will my supply be ok - or will I dry up?
Do you think it is likely I'll encounter engorgement etc?
Will this mark then end of my bf'ing?

Your supply will be fine. Hard to know if it'll be the end of bfing, as it depends in ds, but if you don't want it to be, just offer when you return.
I didn't get engorged

Your supply is so well established now that you should be fine.

What CMOT said

I got engorged when I stopped feeding my daughter. I was only in one feed. Have you got a pump you could take with you?
Personally I would use this as the time to stop feeding but if you wish to continue you'll just have to offer it and see if he goes for it.

You may get engorged if you're prone to oversupply - I never stopped getting tender and full with DS even if away just overnight, and when he finally self-weaned they hurt for days, BUT I appear to be the human equivalent of a prize dairy cow.