DD is 19 months and has missed her nap a number of times. She seems to cope fine however much sleep she has so really we just put her to bed earlier and hope she sleeps through. She does get very grumpy at tea time, but I can't get her to catnap so early bed is the only way to go!
She refused her nap two days ago after a really good night's sleep so we had her in bed for 6.30 - about 45-60 mins earlier than normal. I try to keep the afternoon low key if she refuses to nap too.
Hope that helps!
Laura