Hi folks, San Francisco native here.
This will never happen. I could have seen a scenario where it happened, because the major mistake the California Golden Seals made (besides stinking) was not playing out of the Cow Palace. The NHL, in its infinite wisdom, chose the shiny new Oakland Coliseum over the Cow Palace. Unfortunately that took the NHL Seals away from the big fanbase for the WHL Seals, which lived in San Francisco and the Peninsula. Back in 1967, BART didn't exist and so there was no convenient way to get to the Oakland Coliseum except fighting through rush hour traffic on the Bay Bridge. That dealt a major blow to attendance and put the team on its inevitable course to doom. If they'd stayed in the Cow Palace, the plans to build a new arena which were floated in the mid-70s might have become reality and the Sharks never exist.
As for today? Nah. The hockey fanbase in SF is small, and somewhat fractured. I've sat in bars in the Mission and watched Habs games, then left and gone across the street where people are packed in a bar watching a Penguins-Islanders game. Surprising to say the least. But most locals root for the Sharks. San Franciscans are totally parochial so many of them would probably root for some theoretical SF team, but enough to sell 14,000 season tickets? I doubt it.
The more preferable option would be for the Sharks to market themselves a little bit more up here. The Sharks used to have quite a following in San Francisco but that disappeared in the late 90s. Part of that was that they were basically playing in San Francisco for the first couple years of their existence (the Cow Palace being inches over the Daly City border) and the general increased interest in hockey in general in California. But the Sharks seem to feel like there's no point in marketing north of the Santa Clara county border, and with the Warriors being their usual hopeless selves and the 49ers preparing to flee town there is a vacuum for a winter team to support in SF to complement the Giants, who the city are in a deeply fulfilling long-term love affair with right now. Everyone was following the playoff run in 94 & 95 with even the Chronicle offering front page coverage. That doesn't happen anymore.
They might need to expand that fanbase as well because eventually the A's are going to move to San Jose with the Giants getting their ten pounds of flesh and that will certainly affect the Sharks' bottom line. I'd prefer the A's in Oakland but in reality it's about the A's writing a ginormous check to move down south.