It takes an average of 58 days to hire an engineer in the US. [0] Add to that another two months to onboard them. [1]
> Offer them half your company if that's what it takes.
Wait - so someone accepts a job, implying that the comp was fair. And then quits a week before a start date without any notice (OP's story). Were you recommending that founders should pre-emptively give away half of the company on top of the original offer just to prevent the possibility of any one random person acting dishonestly?
[0] https://resources.workable.com/tutorial/recruiting-kpis [1] https://www.quora.com/How-long-does-it-take-to-onboard-a-sof...