His paintings were shit, they were right to reject his application.
I think they were good enough that Hitler could have made a living, of a sort, as an artist. Perhaps he would scrape by selling his architectural paintings/prints to tourists in Vienna or Munich, maybe with some supplemental income.
Hitler didn’t try very hard to get into art school; it was Vienna or bust. If he really had a powerful ambition to become an artist, he could have applied to architectural school (as suggested) or to less exclusive art schools, or even taken an apprenticeship as a sign-painter.
When he was in Munich, Hitler lived just blocks away from modern artists Wassily Kandinsky and Paul Klee, among others. They represented what art had been becoming since the invention of photography; Hitler had no interest and stuck to his ten-pfennig-a-dozen postcard style.
Both Kandinsky and Klee fled Germany in 1933. Both were represented in the 1937 exhibit “Degenerate Art”.
Hitler will likely serve in WW1 anyway, and I won’t speak to the possibility of him dying. But imagine this: his experiences inspire him to paint the horrors of war, in the style of Otto Dix. Dix was, OTL, hated by Hitler more than just about everyone else. (None of the artists mentioned were Jewish.) Here’s Dix’s “Stormtroopers Advancing Under Gas”, an etching/aquatint from 1924: