All things are possible, including all aviation above paper dart level being grounded on 30th March 2019.
The least likely a/c to be grounded are, funnily enough, microlights as the group of aircraft/licences almost wholly self governing.
Since in the event of a no-deal Brexit, there won't be any AVGAS 100LL, as it's all imported from Europe, there won't be any SEP flying.
Actually, lack of aviation will be the least of our worries. I read somewhere that we're only 24 hours at any stage of a disruption of the supply chain, from food riots and mass looting of supermarkets.
It'll make the poll tax riots look like a Sunday afternoon in the park.
We're buying seeds and marking out the lawn for vegetable beds.
TOO