A: How premises matters should be dealt with when a partner leaves should be in the partnership deed. Normally the deed would require the departing partner to sell to the remaining partner(s) at market value.
When a GP surgery is valued, partnership deeds often stipulate that the valuer must assume the building's continued use as a surgery and that premises reimbursement will continue.
While in some circumstances it may be appropriate for the valuer to take into account the trend of values in surrounding properties, it does not mean that because nearby commercial or residential properties have fallen in value, then so too must the value of the surgery.
GP surgeries are a separate market where value depends a lot on the quality of the premises for general practice purposes. Partnership deeds do not generally state a base valuation equivalent to an outstanding mortgage debt unless the premises are new and their construction cost exceeds the market value.
If there is no partnership deed or it does not include an instruction requiring a departing partner to sell, then any change to the current situation must be by agreement. This means that the practice is in effect a sitting tenant with no legal documentation or lease in place.
You should still be paid your share of the notional rent and you will still be liable for structural and external repairs, external decoration and buildings insurance in proportion to your property share.
Such a situation inevitably leads to disputes, so if you do not sell to the partners, I strongly recommend a lease is put in place to formalise the arrangement.