I've said it before, but Gilchrist really wasn't the first person to be genuine Test-class batsman in his own right plus wicketkeeper. Alec Stewart obviously predated him by several years, and Andy Flower might not have been the best wicketkeeper you'll see but he was far better than some. Sangakkara became the part a couple of years after Gilchrist (he'd been an inept wicketkeeper for his first year or so). Obviously there'd been the odd one prior to the 1990s too - Dujon, Lindsay, Walcott, Ames, etc.
However, it's been a long time since someone could make a Test side purely by being a good wicketkeeper. Rodney Marsh was probably the first in this line of Australians - you saw that by the way Wayne Phillips was asked to keep wicket after Marsh's career finished despite it clearly not being a strength of his. Healy's place may never have been in danger, but how many others were there around who were scoring state runs? (Which, as I note above, Healy actually was on the rare occasion he played) If Phil Emery was first-reserve, I presume the answer is "no-one".
Healy's place was quite rightly never in doubt even before he became the excellent lower-order batsman he was for 59 Tests 1993-1998/99. But if he'd been an obviously inept batsman with better options out there, I don't doubt it would have.
Gilchrist did not start the trend of wicketkeepers being able to bat. He was simply one (the best, in fact) of an exceptionally rare breed. Before or after him, the man who is Test-class batsman and wicketkeeper is exceptionally rare. Most Test wicketkeepers are merely decent lower-order bats, the exact same thing Healy turned into - eventually.