Whether it would've caused the immediate collapse of the USSR's ability to resist is conjecture, however Moscow as an objective was the natural choice, political significance wholly aside. Losing Moscow would've been a massive blow to the USSR, but its outside the scope of this sub I feel to discuss if it would've been fatal.

Moscow was a large military and industrial hub, and a 'communications' center. In military terimonology, a line of communication implies ease of movement of supplies, men and naturally communications; its a carry-over from the days of orders handed by messenger, among other pre-radio communications . Point is, the rail-hub in Moscow allowed the USSR to move around their reserves quickly and along interior lines. Taking Moscow was suspected to be ripping out one of the key crossroads for the transportation of men and material. All of the immiediate objectives for Barbarossa implied destroying enemy forces in and around these large hubs; Leningrad being another prominent objective.

The very first outlines and incarnations of Operation Barbarossa had the RKKA being destroyed in a series of envelopments en route to Moscow, with the final seizure of Moscow preventing a resurgance; essentially stranding and isolating any remaining units in the Northern or Southern routes of advance. Plans changed, OKW suffered from massive over-confidence and over-estimation of the level of destruction being wrought among the RKKA. The dash to Moscow was fatally delayed by a turn south for a battle of encirclement near Kiev; which was impressive, but did little to disrupt the ability of the RKKA to form reserves in the Far East or around Moscow and ship them out in a speedy manner.