1. Resigning from a tenured position likely means taking a one-way street. The exception is a well-known scientist that can easily switch tenure to 2-3 other school today. In many fields competition for tenure is brutal and once you leave you may have some disadvantages in re-entry against a bunch of post-docs. "Only losers leave academia" is still a widely held mindset. All this does not mean not to resign; just be aware.
2. Do you still need money? The fact that the company is not ramen profitable in 7 years (including last 3 years of dedicated effort) means it may not be a source of income for a while. If you are not set for life, how long can you afford to not work? Will you be OK in industry (some professors thrive there some are completely miserable with a manager who tells them what to do and imposes deadlines)?
Unless you are set for life I would seriously consider your 50% option -- you get another year to fully dedicate to your startup without teaching a single day and still maintain tenure. In a year, re-evaluate. My 2c.