So is the reason your director wants to ADR because of bad production sound? What’s the problem with the production sound, specifically? Background noise/fuzz, or something else?
In general, ADR is VERY hard to implement in a way that doesn’t sound like it was replaced after the fact. It’s hard on actors to recapture the magic of the moment, ESPECIALLY when they have to try and perform in time with the video you’re overlaying new dialog over, and it’s hard on the editor to make the new sound, well, sound like it’s coming from that day. The editor will also probably have to completely foley all the background noises so it all sounds consistent, which is even harder.
If there are only a few problem areas, maybe try just ADRing those, and using editing tricks to hide them within the larger sound mix? Without knowing what kind of issues you’re having, though, it’s hard to know how difficult it will be.