When you are mixing with downward expansion and the downward expander creates holes during the fades at the ends of dialogue regions, what do you do?
When you are experiencing holes or gaps in the audio, use fills, turn the expansion down a notch or turn the expansion off alltogether. If it does too much, it might not be the right plugin at the moment. Too much processing is always worse than too little processing. You can always automate the bypass.
I normally don't use expanders, I manually write volume automation and use noise reduction instead. Should i use an expander, it would be a multiband expander like the Waves C4, it has a lot less of the "pumping" sound.
In my experience, it's best to use expansion on dialogue lightly; around 6dB max. And make sure your fill and/or sync fx tracks are going through the same expansion. That way, it should just rise and fall with the dialogue, and not draw attention to itself by pumping too much.
I concur with Rodger - try messing with the attack and release settings to slow up the drop.
The other option is to use fill between the dialog regions. This is the way I cut dialog. Grab some "room" from another take not used and fill in your gaps. This allows for a smooth scene.
aaand increase Release time a little.