If your ex-business partners owes back taxes, they can come after his assets to collect. Those assets would include any property that he owns. If he owns part of a business in which you are also an owner, they could come after his share of the business, but not after your share.
Yes, it is possible to go to prison for tax evasion. Generally, the taxes owed are a civil matter, but if there has been fraud or misrepresentation to the tax authorities, they can bring criminal charges which could result in imprisonment.
Generally, the IRS would not be the one to revoke a contractors license. It would typically be the state contractors licensing board. If he is still working, you can file a complaint with the Washington State Department of Labor and Industries.
Here is their link to report an unlicensed contractor. You can do it online following this link:https://fortress.wa.gov/lni/rts3/
Similarly, if you are operating without a business license, that license is issued by the municipality, so you would go to the city that issued the license, or in which the business is located, and file the complaint there.
Good luck to you. I wish you all the best.