Sign a free agent
If Whitworth doesn’t come back and the Rams aren’t confident in any of the players currently on their roster, free agency is an option. Anthony Castonzo will be a top target if he doesn’t retire, while D.J. Humphries is a younger player (26) who should get plenty of looks in free agency.
Humphries would be a downgrade from Whitworth, but he’d also be a cheaper and younger replacement. Perhaps Aaron Kromer could help him develop into a great left tackle, but the Rams shouldn’t bank on that happening.