I don't think multinationals moving away will have such a massive direct effect on the real estate market. Many expats are on short term contracts and thus not owning property. Those that aren't are probably over represented in higher income categories and thus not competing for an appartment in the price range you mention.
What may have a far bigger effect is the exchange rate. The EUR going from around 1.60 to around 1.10 has put enormous pressure on exporting companies and made it easier for imports. One reason the CHF is so strong is that people from across Europe and the world see it as a safe haven in uncertain times. Even if they are just stashing 1000 CHF notes under their mattress. And those uncertain times are not over yet. If the exchange rate slips further we may see many companies go broke or move out of Switzerland. This will lead to higher unemployment and will bring down the property market.