First off there was already a understanding that the US and Brit armys would meet the Soviet armys somewhere west of Berlin. So, you have to specify under what circumstances the Western armys would advance east of their assumed Area of Operations to Berlin.

Second, the original assumption by the Allied leaders, including the USSR was that Germany would be jointly occupied and governed as a single entity. Rather than split into four independant occupation zones. The zone system emerged postwar from inter Allied squabbling, and had as much to do with French views as Stalinist plotting.

The most likely result would be the western army leaving the Berlin region a little after the war and the occupation zones established as historically. The next likely result is that the French idea would be dropped and a single joint occupation be established. This is to the Soviet Unions advantage as their occupation authorites can loot all of Germany and support Communists locally everywhere.

Assuming a result where Berlin is included in a US/British occupation zone. With the USSR holding only a token part, or nothing of Germany. then the Cold was has its frontier a couple hundered kilometers further east. The USSR may be reluctant to evacuate Vienna in return.