As yet unknown.
But we're likely:
1) to have some difficult moments regarding our support. Financial support is given in pounds sterling and we are paid in euros. If the pound flourishes as predicted then things will be great. If the pound languishes as predicted, then things will be very tough.
2) to lose the right to drive - at present we don't have to exchange our UK licence for a French one, and I am reluctant to do that for the sake of ten years' service. If we get back to the old situation where you have to exchange your licence, then I'd rather just lose the right to drive here.
3) to need a carte de séjour. A residence permit. I am tempted to apply for one now. They last ten years, so if we apply for one now it could take us up to retirement.
4) to rethink retirement - at present we are heading back to the UK in ten years' time. However the UK may change a lot over the next few years. What will the NHS be like with all the new funding injected into it? How will Wales fare? What will happen to house prices? How will Brexit affect our UK state pensions? My UK pension plans? Our French pension?
Whatever happens, God is sovereign and I'm sure we'll be OK.
But obviously we'll have to take decisions based on how the situation unfolds.