Don't get legal advice from coders.
My guess: if you break the terms of a licence (not a contract, as has been pointed out) then the other party could go to court and get an order or injunction to stop you selling your software until the GPL code portions are removed. If you were to disobey the courts then the courts may well be able to fine you, send you to jail etc.
I can't begin to guess how likely such an outcome would be.
There do seem to be many less onerous licences than GPL, and lots of good stuff under those licences.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
