1) Collapse of opposition strengthens Johnson's hand in resisting US demands. He won't be as desperate for a fast deal.
2) Tory Party can now pass literally whatever it wants, including if it loses some votes to do so.
If you were concerned about areas where the US had offensive interests the Tories oppose, you can be less worried.
If you were concerned about areas where a US FTA might be the vehicle to lock in things the Tories want to do anyway, you should be more worried.
1) Where the newly elected or returned Tory MPs fall on the spectrum of Singapore-On-Thames Libertarianism to Made-In-Britain Protectionism; and
2) How much influence rank-and-filers will have on Tory trade policy.