They have enough cash reserves to last 3 years without any income. But 15% of income is Google free. If Google disappears, they will surely get an income hit, but someone else will gladly pay some price for that position, perhaps half of what Google is paying. People are really blowing this out of proportion.
Both Bing and Yahoo have outbid Google in certain countries in the past. There’s a new wave of AI powered startups with tons of venture capital. I could imagine them making sizable bids.
But I get what you mean. The main difference to your scenario is: search money will definitely not totally disappear, Mozilla has huge savings, and they can just finally pivot and focus on making a real premium offer that people would want to pay for.