This hasn't happened to me but I want to avoid it. So here's the simple scenario:
1. You use LastPass to generate a password for your main email and do not memorize it.
2. You have multifactor authentication on and you lose that device.
3. You try to get into your LastPass and it allows you to turn off multi-factor authentication, sends you an email on your main email address to get back into your vault, but you do not memorize the password for your email anymore.
4. You're screwed?
Is there a way to work around this case and get back into your vault?
I can see that if you were still signed into your email on another device you might be lucky and be able to receive the email to get back in but that isn't a solution for this. You can also try to memorize/write down the LastPass generated password for your email but that kind of defeats the "Single password to memorize" purpose of LastPass for me.