I'm thinking if Curly came back, Shemp *maybe* would have gone back to working with Abbott and Costello? (He was in quite a few of their movies if I recall correctly).
Shemp's solo career is always incorrectly "defined" as working with A&C and W. C. Fields. That only scratches the surface.
From 1933 to 1949 Shemp appeared in 103 films on his own, both shorts and features.
Shemp's work with A&C was due to his being under contract to Universal during 1940 - 1943. When Shemp's contract was not renewed, his Universal Studios work with A&C ceased, IT AIN'T HAY (1943) being the last; he only appeared in 4 A&C features (plus 1 PSA newsreel cameo). The exception was AFRICA SCREAMS (1949), an independent film Bud & Lou made at Eagle/Lion Studios, and released thru United Artists; Shemp (and Joe Besser) costarred in that film by A&C's choice.
Prior to Universal, Shemp did 30+ shorts at Vitaphone from 1933 - 1937, many which will be released thru the Warner Archive in 2011. He had a short tenure at Columbia 1938 - 1940 as support for Andy Clyde and Buck Jones; and a loan out to MGM for ANOTHER THIN MAN.
Shemp worked busily at Universal during 1940 - 1943,
not just A&C and Fields support. He costarred in the TechniColor Hall/Montez ARABIAN NIGHTS (1942), and numerous "B" comedies, dramas, and musicals with the Andrews Sisters, The Dead End Kids / Little Tough Guys, Lon Chaney Jr., Broderick Crawford, Olsen & Johnson, John Wayne & Randolph Scott, more...
He returned to Columbia in 1944, starring in his own short subjects, and support in the occasional feature film. He also had access to other studios, like Monogram where he made 3 features with Billy Gilbert and Maxie Rosenbloom, and a feature at Republic with Pinky Lee.
Bottom line, Shemp had a long, impressive resume. If Curly had returned to The Three Stooges, Shemp would have resumed his solo Columbia shorts series. Anything beyond that is pure supposition/conjecture, but at the very least, Shemp's credentials probably would have given him plenty of future work in film and television.