I played a campaign of Pike & Musket Early hard I guess, playing as Italians. All was going well, and I had conquered about a fourth of the map, when I did exactly what you did. My Monarch invaded Sardinia and got stuck. The rebels were all over. Having plenty of troops I held on to my empire, but my income turned negative. Stubborn as I was I didn´t start abandoning troops until some 10-20 years later, realizing I would never get the money to buy the port otherwise. Took another 10-20 years to repay the debt and get my economy to a positive sum. Probably I had fun.