Carrying 3 goalies would be a horrible idea. Wherever Askarov is, he needs to be playing regularly.
Both of our current goalies are only signed through this season. If Askarov makes the Sharks out of camp I'd expect one of them, likely Vanacek, to be put on the trade block or waived.
They'd probably get a lot more for Blackwood via trade, so that's an option too.