Not much to say about this that hasn't already been said. There are plenty of clues that point to Bush blowing off Guard duty for most of 1972 and early 1973, and then having to do some fancy footwork to keep from getting shipped off to Vietnam for dereliction of duty. The missing records might have merely supported what most people already think, as well as put paid to Bush's claim that he did duty in Alabama (but then details in his story have already changed several times without consequence). Basically, the issue comes down to credibility--who does one choose to believe?
I will note that the Bill Burkett claims, overhearing a Guard general and then-Gov Bush aides discussing "scrubbing" Bush's TANG record in advance of his re-election campaign and later witnessing Bush records being tossed, took place in 1997--about the same time as the relevant microfilm met its fate. It is not inconceivable that a coordinated scrub effort would encompass both paper records in Texas and microfilm in Denver. Especially when you're a Bush family member and presidential visions are already dancing in your head.