Well, if you get caught they will put a stop work order on it and make you wait until you get full architectural drawings and permit approval. You would have to pay a penalty for starting the work without a permit, which could be pay double the permit draw amount.
You could pull the permit now, before the city finds out and just pay the regular permit fees. The stated value of the repairs/remodel are used to help reassess the property for taxes when the tri-annual reassessment rolls around for your area.
You could, theoretically finish the work as quietly as you can. Properly dispose of construction materials, not in the alley, but it is hard to hind a dumpster and for all anyone knows dumpster companies report usage to the city. Or if you work at odd hours and annoy the neighbors, the could report you.
Many people get things done without a permit, but are you doing the work correctly, did you remove anything structural of affect safety with water and electric, will a future buyer go to the city for proof that the work was done correctly and permitted. You could lose part of the value of unpermitted work if a buyer has an issue with it.