There was a discussion in the comments to a post over at Arctic Ice Hockey a couple of weeks ago about whether Tampa's goaltending (current team mark: .896) will regress back towards league average over the rest of the season. Over time goalie save percentages will nearly always move towards a goalie's career average. At the moment, Mathieu Garon is playing at close to his established level (.907 this season, .904 career) while Dwayne Roloson's seasonal rate is well below his career mark (.883 and .909 respectively). It looks like it is reasonable to expect major improvement from Roloson, which should boost Tampa's numbers the rest of the way.
However, while I am confident that Tampa's team save percentage will continue to move upwards towards league average, I do not believe this will be because Roloson's numbers will get a whole lot better. It will instead occur as the team shifts more playing time to Garon, who started 11 games to Roloson's two during the month of December, or perhaps through bringing in another goaltender if GM Steve Yzerman decides to address his team's crease situation. Roloson's numbers will probably improve, if nothing else playing in more of a backup role against weaker opponents may help slightly, but the reasonable expectation is that at 42 years old he is simply too old to expect him to produce anything north of .900.
Looking at the career records of goalies in the save percentage era past the age of 40, it is impressive how much the top two on the list stick out both in terms of quantity and quality of performance:
Hasek: 3366 shots, .914
Roloson: 3602 shots, .907
Everyone else: 4899 shots, .891
Hasek and Roloson each have two of the top four seasons among the 40+ crowd. Other than them, Ed Belfour is the only one who managed to keep his starting job past the age of 40, although his numbers were much lower. Everyone else had numbers that were below league average, in most cases well below.
1. Hasek, 2005-06: 43 GP, .925
2. Roloson, 2010-11: 54 GP, .914
3. Hasek, 2006-07: 56 GP, .913
4. Roloson, 2009-10: 50 PG, .907
5. Joseph, 2007-08: 9 GP, .906
6. Belfour, 2006-07: 58 GP, .902
7. Hasek, 2007-08: 41 GP, .902
8. Burke, 2006-07: 23 GP, .901
9. Belfour, 2005-06: 49 GP, .892
10. Roloson, 2011-12: 17 GP, .882
11. Joseph, 2008-09: 21 GP, .869
12. Esposito, 1983-84: 18 GP, .859
Based on those comparables, a good bet on Roloson's current save percentage talent is probably in the .895-.900 range, although with perhaps 15-20 starts remaining Roli's actual performance could still vary quite widely.
Assuming Garon keeps up his current level of performance and keeps getting the majority of the starts, Tampa's save percentage will probably improve by something like .010 the rest of the way. For example, if Garon keeps his .907 through the end of the season while Roloson plays at .895 and the shot split between them moves from the current 57/43 to 67/33, the Lightning should end up with a save percentage of .903 over their last 50 games. That's still well below league average, which is why the team should certainly consider making a move if they want to make a stronger playoff push this season. History suggests their current goaltending will be unable to perform at a league average level, which will make it difficult for the Lightning to catch up in the standings.