Radio frequencies can't be 'switched off'. They can only be made legal or illegal. (i.e. your church's microphones will continue to work, irrespective of any decisions by Ofcom, but you need to ensure that the relevant radio frequencies can still be used legally).
I've searched Ofcom's website (& elsewhere) and I can find absolutely nothing to suggest that the current 'license free' VHF frequencies allocated to wireless microphones are due to change. However there are moves to change the frequency allocations of
licensed UHF wireless microphones (to which many theatre professionals, including Andrew Lloyd Webber, have strongly objected). I suspect that's where the confusion has arisen.
So I'm confident that your church can continue to (legally) use its existing VHF microphones. That view is supported by the Anglican church authorities in Newcastle, who have added this info sheet to their website:
http://www.newcastle.anglican.org/userfiles/file/e-Bulletin%20downloads/Radio%20Mic%20Changes%202012.pdf
If you're still worried, ask Ofcom:
http://www.ofcom.org.uk/contact-us/