this way my company cannot send me back to Poland.
If you want such a ban, go to the airport, speak to the border guards and explain the situation. I'm almost certain they would have no problems with banning you from Schengen for several years.
Is it very likely they will tell me not to return or give me the stamp that says I overstayed?
If you don't draw attention to yourself, it's a 50/50 chance. If you tell them - then you're almost certainly going to get banned.
You are hugely unlikely to get put in prison.
I don't think they even use prison as a punishment for overstaying - as I recall, those that come in through Ukraine are sent to some horrible detention centre in Ukraine. Not sure about Belarus/Russia, but I think they're kept in secure accommodation until they can be deported - but someone from the US, they're just going to throw on the plane, surely?
I'd go with what Teflcat said: when you get to the airport report yourself for overstaying and ask them if they can let you off with just a one-year ban for overstaying.
Heck, he might want to ask for a several year ban ;)
(that'd be a first - "Sir, please ban me from Schengen for 10 years, my boss is insane")