Hi! I’d use “pa rin” over just “pa” if there’s a longer time involved in the “wait” or “process” (like if it’s taking longer than expected.)
Example 1:
A: Dumating na ba siya?
B: Hindi pa.
(10 minutes later...)
A: Ano, dumating na ba siya?
B: Hindi pa rin eh.
Example 2:
“Kahit anong pilit kong kalimutan ka, ikaw pa rin ang laman ng puso ko.”
Example 3:
“Manalo ka man o matalo, ikaw pa rin ang kampyon (champion) para sakin.”
For examples 2&3, it’s like “after all is said and done...”
I guess “pa rin” can be translated to “still”, like for Example 1, (B) would say, “He hasn’t arrived,” and then, “He still hasn’t arrived.”