First of all, this "again" stuff is nice, but the Pats haven't gone 19-0 yet THIS year, to be technical.
Second -- yes, the team could be approximately as good next season as it is this year. It can't be as good THREE seasons from now, for cap reasons, but NEXT year is still doable. That was a good point above about Brady still having the potential to get better with the receiver corps, and of course Maroney can still get better as well.
Third, it's been a pretty lucky year. A few games could truly have gone either way. What's more, the injuries have been relatively mild in magnitude and pretty well spaced across the season and roster. How many player-games have there been of eye-roll JAGs starting or playing near-starting roles like nickel CB (e.g. Rivers, Spach, Baker, Eddie Jackson)? I think it's been a lot fewer than in prior seasons, when both the secondary and the WR corps were routinely decimated.
Fourth, it's likely that the Colts are going to do something to reload, even if it means deviating from their traditional lack of reliance on FAs. That's just two games (one regular season, one postseason), but it's still a consideration.
So don't be shocked if the Pats are the clear class of the league again next year. But even so, don't look for two straight years of 19-0.