It depends on the relevant airline rebooking policy, but time-critical matters (like vacations) are one basis for getting priority when facing rebooking, whether with rerouting or on OAL (another airline). Naturally, airlines will give priority to rebooking on their own metal (hence why, if time permits, they'd re-route via SFO rather than rebook on another airline), but if this is problematic, then rebooking on another airline is possible, particularly if there are seats in an equivalent fare class (bucket of seats, rather than booking class like economy).
https://thepointsguy.com/news/aa-clarifies-how-pax-will-be-rebooked/ is a good article that explains how it works for American Airlines...