It shouldn't surprise you to hear that, in the end, Sierra's offer wasn't followed through. There were first-person games before id's effort, there were better games with more longevity since-most from id itself-but Wolfenstein 3D was the game that kickstarted everything, and made established publishers have a ‘holy shit' moment that made them slap $2.5 million dollars down on the table.
It's difficult to understate how impactful a game Wolfenstein 3D was-how much it changed things, how it raised the bar, decided it still wasn't high enough and so tore it off and threw it over a mountain. Wolfenstein 3D was so good that, when id Software took an early version to Sierra in 1992, the publisher quickly tabled a $2.5 million offer to purchase the pre-Doom dev studio.
