I believe around 25% of tourists to Spain are from the UK
https://en.m.wikipedia.org/wiki/Tourism_in_Spain
So perhaps 3%of GNP
How many Brits would be put off by having to take out health insurance... I'd guess not that many as they will have to take out the same healthcare wherever they go and most won't want to stay in the UK for holidays.
At worst perhaps 1% impact to GNP
Spanish economy growing at 2% so even if they don't figure a deal out it's hardly likley to be too impactful even presuming less Brits and more free rooms wouldn't just result in some cheaper rooms sold to other nationalities
Probably they will find a deal but it's not critical for spain they do