Commercial Real Estate Valuation Dilemma

[William Bonnet]

Hi this is the situation and I'll try to make it as simple as possible:

I am part of a group of physicians who, through a corporation (let's call it Realty Corp) own a medical office.  This office is is leased to a clinic with whom we also have a professional service contract through another corporation (let's call it Medical Corp).  We had 7 year agreements but have less than 12 months left and due to change in management, the possibility of renewing another lease and service agreement and the details of the agreements are uncertain although we believe we should be able to work something out.  

In the meantime we have a physician who is retiring in a year and another who is joining both the Medical Corp and the Realty Corp in 6 months - we make it a requirement to join both.  There is no buy-in for the Medical Corp. However, the main dilemma is in the valuation of the Realty Corp buy-in and buy-out because from what I understand, the medical office would be much more valuable with a 7 year lease in place (and the tenant is reliable and reputable) than if there is only a few months left in the lease or no lease at all since the market.  Prior valuations have been based on income approach (using expected cash flow with reversion at end of holding period) which was significantly higher than the comparative sales approach by about 15-25%.  

My questions are:

1) All else being equal, how much value is there in having say 7 years left on a lease vs 1 year?  I suppose it depends in part on the value of the lease compared to the value of the property if it were to be sold.   Since the income approach continues to be higher it means the property has more value as a rental property assuming we can renew under similar terms.

2) How can we structure the buy-in and buy-outs to be fair to everyone if the valuation could change significantly within a short time frame depending on the outcome of the negotiations and details of the lease?

Hope this make sense but I'm happy to add more details or answer questions.