Provided you will not receive any ownership or interest in the business, until after he passes, you'll get a step-up in basis as others have mentioned already. One thing that will be needed and probably required, is a professional appraisal and valuation of the business as soon as possible after his passing, and before any large transactions are executed after he passes. Most likely, the IRS would not agree with your dad's valuation, or your own valuation for that matter. Therefore, you need to plan on paying for an appraisal (which can be paid by the estate after his passing) as soon as possible once he's gone.
As others have mentioned, you really need to get with an estate planning attorney on this, *before* your dad is gone. If you're in a state that taxes personal income, or if dad is married and lives in a community property state, things can get very complicated, very fast if you wait until "after the fact". The complications are compounded even more if there is not a will in place too.
