It's not only a launcher issue (and given the timeline, switching launcher is unlikely feasible even if the rocket is available). The descent module is russian made (with ESA bits in it), so the rover is now stuck. This launch window is dead.

Stopping the partnership with Roscosmos means redeveloping a descent module and either collaborate with NASA/JPL or develop new technologies from scratch in Europe. Even 2 years is optimistic for this.