While it has some degree of canon based on the novel, where Palpatine orders Jerjerrod to destroy Endor if the shield falls, I don´t see it working here as it worked in ANH:R... In ANH, my impression is that when Luke´s torpedoes finally hit the DSI core, the whole thing blows in a moment, so showing the super laser about to fire still makes sense.

But in RotJ, to show the tension of the the MIllenium Falcon escape, the explosion is quite slow and Luke and the MF literally escape through the flames; the super laser would simply not be in conditions to build up and fire at all... What might work if not breaking the pace of the film (ESB:SE scape from Cloud City comes to mind... eekkk) would be first having Palpatine giving the order to destroy Endor; then later Jerjerrod giving the firing order, followed by the "commence firing ignition" sequence just before Wedge and the MF arrives at the main reactor and hit it...

A lot of effort to make it work nicely, I´d say just remove the ring when the DSII blows up; I don´t hate it but with the MF still in the scene having the ring overtaking her just looks bad...

And in a side note, while there are a lot of speculation that seems to confirm the DSII size, I find the 900 km number ludricous... :)