I have a cx 50 crank double if I lose the small ring and front derailleur will I need something to stop chain skipping like on my mtb

Yes. Probably.

sling a n/w ring on?

I have that chainset and use a raceface N/W with an Ultegra mech, the chain retention is good – I’ve dropped it once, in a very sticky muddy race. The only negative is that you have mount the ring on the outside so the chain line isn’t great at the larger end of the cassette