And the Alerted Japanese would say "Hey those Bombers flew ---------> that way" and send everything they had after them would of been a very BAD thing, second those B-25s launched those carriers were full steam back to Pearl, they were far to deep in enemy territory to waste valuable time picking up survivors.
To add, it wasn't just the USS Hornet with all its chips being put on the table, the Enterprise (escorting, since the Hornet's deck was crowded with B25s and its fighters trapped below) and a large number of cruisers and destroyers.
Had either of the valuable ships been damaged or disabled by one errant pilot or sub after being spotted as they lingered deep in enemy territory, the rest of the fleet would of had no choice but to of continued a full running retreat and could write off any damaged ship as a total loss if not by their own hands then by the Japanese within 24 hours. Even one destroyer would equate to a larger loss strategicly and materialy than the bombers and their crews, the later which already ceded to taking on a risky mission with little chance of a quick return home if any at all.