I work on the basis that I don't want to have to deal with any whinging, crying, clinginess and all the other trappings of an over tired toddler.
If he can go from waking up through to, say 6.30pm without showing signs of being tired, then go for it. I wouldnt being bedtime any earlier than 6.30 though, because of the effects on get up time in the morning.
If he is a handful though, then you dont need to power through just so he manages without a nap. That's not good for him, if he needs sleep then he needs sleep.
I've known children sleep 14 hours at night and have no nap, just 6pm-8am solid sleep. That's fine, but I'd imagine rare. If your DS has a big, long night sleep then maybe that's his natural sleep cycle.
In your position I would firstly just give it a few weeks without changing anything. It's just been Christmas, loads of colds and sore throats doing the rounds. He might just need time to settle back into normality.
Then I'd still an issue, I'd move around the routine. I'd probably make nap time an hoir earlier and limit to an hour at first - so 11am-12pm. See what that does.
It is not unusual that there will be backward steps when baby needs more reassurance to sleep than they had previously. Lots of things cause thesebackwards steps. I'd go back to reassuring to sleep and then gradually extract myself again over time.