Well it happened again recently (Martyn, Warne, McGrath, Langer and then soon after Gilchrist) and it doesn't seem to have done any real harm.
Why not? Because the replacements have been up-to-scratch. The trouble '84-'89 wasn't that Chappell, Marsh and Lillee all left together, it was that this happened, then Hughes, Yallop, Wessels, Hogg and Alderman went on Rebel tours, then Lawson got injured, and the David Hookeses, Steve Smiths, Graeme Woods, Andew Hilditchs, Wayne Phillipses, Tim Zoehrers, Greg Dyers, Simon O'Donnells, David Gilberts, Tom Hogans, Greg Matthewses, Bob Hollands, Ray Brights, Murray Bennetts, Peter Sleeps, Peter Taylors, Tim Mays, Trevor Hohnses and more (including initially the David Boons, Stephen Waughs, Craig McDermotts and Merv Hugheses) simply weren't good enough.
And there's nothing you can do to control how good the replacement players are. And you won't make them any better by making older players carry-on a bit longer than they'd be best-served doing.