Doug:
You are correct, the Lilloeet river probably peaked 2-3 weeks ago, however as I seen it on last Saturday, it is still very high.
The Pemberton Valley is not very wide and there are number of farms/residences on both sides of the lower Lilooet river and it is these properties the initial concern is about. Depending on how big the newly created dam is upriver and what duration it may be there for and if gives way will provide a better answer on the severity of any flood damage. The overall problem if that dam decides to let go all at once is there is only the main road into the valley and it is a secondary 2 lane at that. At many places, the road is right along side the Lillooet River and it would not take much to have the river overflow it's banks in some places.
I know this area very well. At around the 17 km mark from the town of Pemberton is a turnoff to a 1 lane forest service road
bridge which crosses the Lillooet River that takes you (NE and steeply) up into the Hurley River pass (where we were last Saturday). Depending on the outcome of the situation up river, if I were in that area, I would sticking close to that bridge and on the NE side of it. At least on that side, there are a few different FSR (Forest Service Roads) and trails that would take you to higher ground in a very short time. If that bridge gets taken out, the drive over the Hurley pass and over to the town of Lillooet is a long and adventerous drive by car and eventually before you reach Lillooet, you will be right in the middle of an active forest fire area...so you cannot really win...
Hopefully it will not come to this. Be interesting to see what is on the 5:00 pm (Pacific) news. I'll give an update after I watch.
We are planning to be up in that area on the Aug 21-22 weekend and will see if I can get some updated photos of what the mountain looks like now.