How many flights are there from BOS to your destination in the AM on Mondays?

If your're on an 8am outbound that gets cancelled and the next scheduled flight is 2pm, then fly the night before. If there are hourly departures, then take the first one Monday AM.

If you're worried about major weather systems (i.e. getting snowed in) there's always the chance that late Sunday flights will get cancelled as well and the delays dragging well into Monday. You can ALWAYS think up scenarios where the best laid plans will fall apart.

I say fly on Monday AM and if something major happens hopefully the client will realize that you truly did plan your travel with care but was hit with something beyond your control.