I haven't been since 2016, so here's my best guess.

You can go to the swim start via D44B through Villard-Reculas in the morning.
I recall there not being much parking at the lake though, so you may be in for a long walk if you can happen to find a spot.

The roads aren't closed AFAIK, but maybe temporarily around Lac Du Vernay until the participants have cleared?
If you really wanted you could follow your husband on the entire bike route, but that might be a bit much.
Maybe roll down to Bourg-d'Oisans and find something to do for a bit?

I followed my wife up AdH and parked every couple of turns to cheer her, but she was BOP and the traffic and competitors were pretty light.
If your husband is faster it might make sense to head straight up to the village and wait for him to arrive in T2.

The run is pretty easy to spectate as is it's multiloop.

I can understand but what a terrible idea... Even if it's the BOP, even if the traffic is pretty light, the race course should be kept as car free as possible. Being repeatedly overtaken, constantly hearing the engine, inhaling fumes is a major annoyance in a race when you try to focus on your effort and/or take in the scenery.

Dude, there were like 5 competitors around her. I cheered them on, poured cold water on them. They loved it.

Also, do you have any idea how much traffic there is in France? SMH

I do, as I live there.
Look, I've had to endure that on multiple mountainous races (Embrunman, Ventouxman, Altriman...) and I've always found it to be annoying. But maybe it's just me. Sorry for the comment.