Even if Rommel reached Alexandria or the canal, he'd still be facing the Empire forces he had pushed back to Palestine or Sudan or wherever - unless he inflicted some sort of Cannae on 8th Army. So I think the rationale for Torch would still exist. It was still the only way to get significant American forces into action on the European side of the war before mid-1943, and it was consistent with the British/Allied policy of securing Vichy territories for the Free French. As it was, Torch had the ironic effect of giving Rommel's Panzerarmee an added lease on life. Historically, by January 1943 they were pushed back to Tripoli and the border with Vichy North Africa. Rommel - and Hitler - would have faced a choice between surrender, internment, or being the first to violate Vichy territory and undoing the armistice.