As long as the pushrod and lifter (hydraulic flat tappet) are fine, to do an oil change, buy a new rocker arm, pivot, keeper & bolt install it and see how it goes?
I would. Odd that just one would fail like that but not unheard of. Possibly installed wrong (too loose/tight) to start with? You might want replace them all........ to be safe.
Do a full redo of valve lash..... obviously.
