Mace Coronel (Dicky) left the show before the filming of the last five episodes of season 4.
If the episodes are broadcast according to the filming order, his last appearance should be in S4E09 "Quadbusters".

But, according to this article:

"Greene reveals “NRDD” will explain Coronel’s exit towards the end of Season 4 by sending his character Dicky “on a little trip” to Australia and “that’s pretty much it.”

This then could happen in S4E11 "Quadcodile Dundee", so the episodes will be shown out of order?

These are the last 5 episodes of the show:

S4E10 "We'll Always Have Parasites"

S4E11 "Quadcodile Dundee"

S4E12 "House Crushing for Dummies"

S4E13 "Quadspiracy Theory"

S4E14 "Lasties with Firsties"