From there you can get more specific on what "operate" means (i.e. will layoffs occur before scaling back hosting costs).
Has there been any such analysis?
The question as I understand it is is "if no other money comes in how long could Wikipedia operate?
If you assume (and I do) that the Wikimedia foundation (WMF) would keep on the spending path they are on, it would take a year plus or minus a few months to go completely broke. If they were to immediately respond with massive spending cuts they could last a lot longer.
The reason I don't believe that the WMF will react to a revenue decrease with spending cuts is because they really, really, believe that everything they are doing and everything they have planned is absolutely essential. Plus, it is human nature to say "this is temporary. The revenue will go back to increasing next year", all the while greatly expanding the fundraising appeals.
Employee cost has grown 300. How many employees are there? What do they work on?