Yup, by the time the SE came out in theaters he was already about to film TPM. So if the SE bombed its not like he would or could have backed out of the prequels. The SE was put into motion around the same time as the prequels, roughly 1993. This in itself however was likely a result of the mega-success of the Star Wars rennaisance which began in 1991 after Heir to the Emperor.