You charge the EV before the weather event. Not during.
Then when the weather event comes, you still get electricity at home supplied by your car. If the weather event is localized, drive your car to a place with electricity and charge it there and drive back. It's the best.
My concern would be draining the fuel reserves in a vehicle to power my home reduces my mobility. It seems like mixing objectives and in an emergency, I want to keep my super spare backup if I needed to flee.
So you're worried about a weather emergency that takes out your power, followed a few days later by a second emergency that requires you to evacuate a long distance?
I don't think I'd do very much to prepare for that scenario.
It can be the same emergency. It doesn't have to be a second one.
You might plan on riding out a storm, thinking utilities might be out a day or two max. Day 5, still no utilities, no known date for resumption of services, and supplies are running extremely low. How do you get out?
In the best case: Just deal with it proactively. Watch supplies, try to stay informed. You mitigate what you can to stretch things out (making French toast in a skillet outside on the BBQ grill in the aftermath of a winter storm may be the best way to use available energy and feed people a tasty meal, even if it does seem absurd). Plan to leave before things become unmanageable, and adjust that plan as things change, and be willing to resolutely execute that plan before things go from bad to worse.
If you forecast that your supplies will be very slim on day 5, and you haven't left for greener pastures by day 3 or 4, then the the worst case is already unfolding. GTFO before the worst-case ever happens.
But in that worst case: One can call on someone else for help. This is one of those situations where it's time to cash in some favors, and/or where it pays off to always be friendly and helpful with to the neighbors even if they really seem like a bunch of assholes. (The time to start being friendly with the neighbors is right now, by the way.)
(My own backup plan only keeps me rolling both semi-comfortably and independently for about 24 or 48 hours without power in the winter, so I'm leaving after the first night or ASAP. I don't have the complications and niceties offered by something like an F-150 Lightning, but finite resources remain finite no matter their form.)
You're either not going to have much meaningful backup power or you're not going to have much usable range if your plan is based on consuming the energy on your car while holed up and also using that energy to potentially drive a couple hundred miles. That's my real point here.
I think it's more about the long tail of situations that I'm not really able to imagine, or feasible emergencies but ones where my assumptions aren't valid. So not about a specific situation, more on principle that I want to keep my "get the heck out of dodge" energy store separate from my "hunker down" energy store.
I admit it's less efficient to have 2 energy stores, but given we're already discussing potentially life threatening situations, I'm not really looking to optimize for anything except having as many resources as feasible on hand.
Agreed, there are tradeoffs. But from a principled perspective I recognize the risk in having to choose between escape and home power. Adverse events often stack in unexpected ways at the worst time.