It has been 10 days since one of these chicks has passed (thank goodness!

we still have the 6) at what point is it safe for them to be introduced to the rest of the flock? They have been treated like Typhoid Mary up until now out of fear whatever was killing them was communicable, but they have also outgrown their brooder and need to be outside now. I came home later one night and one was roosted up on the edge of the trough which means it is time to graduate. Any advice or suggestions are welcome and appreciated.
I'm glad they are doing better!
How long to wait before introducing them to your other chickens is a good question. Of course it's hard to answer because you still don't know what the problem was.
Since they have gone 10 days already since the last death, if they seemed healthy all that time, I would probably just introduce them whenever it is convenient for you.
My reasons for that:
--Some things are not contagious anyway. If they died of something not contagious, the sruvivors are no danger to your other chickens, so there is no need to wait.
--Some contagious things are carried forever by the survivors. If they had something like that, your other chickens will be infected when you introduce them, no matter how long you wait. The only "safe" thing in that case would be to cull all the chicks. But if you aren't going to cull the chicks, introducing them sooner vs. later will not make any difference.
--Some things are not contagious after the birds recover. If the current survivors have seemed healthy for 10 days, that is probably long enough for such a disease.
So for the three options I can see, in one case waiting is not needed, in one case waiting does no good, and in the last case you might have waited long enough already.
It is also difficult or impossible to keep two groups of chickens completely isolated, so no germs can pass between them. So putting them outdoors but away from your other chickens would probably not cause any harm, but might not do any real good either.
(Other people might give other advice.)