Hi - the MVA is the difference between the nominal value (nv) and the surrender value. FF would calculate the surrender value (sv) based on the current value of the assets backing your policy with some allowance for smoothing (which could be zero). The MVA could increase or decrease depending on how the sv moves relative to the nv. The nv may be static or it may increase (it depends on the policy terms and how bonuses are declared). Lets assume the nv is static, the MVA will reduce if the Gilts, property and equities backing your policy increase in value (for simplicity we'll ignore FF charges + smoothing adjustments).
The question you might want to consider is could you get a better future return elsewhere by investing the current sv in an alternate investment vehicle. The nv does have a value ..... on death - so you would be giving that up by surrendering.
In summary - the MVA will disappear if the assets backing your policy grow to such an extent that the FF calculated SV exceeds your NV. No way of predicting that with certainty I'm afraid.