It was definitely a small sample size with Dekeyser, but I think him being 24 years old and playing 4 years in college helps with that. He's not some 19 year old kid. I also think his performance last season is being understated a bit. It's in great part due to Ericsson's injury but Dekeyser was arguably the 2nd most important defenseman on the team.
Among Wings d-men:
23 points, only 5 of which came on the PP. (2nd only to Kronwall's 49, 25 of which were on the PP)
21:38 minutes a game (2nd only to Kronwall's 24:18)
averaged 2:13 per game on the PK and 1:34 on the PP
+10 (tops among Wings defenseman)
30 PIMs (lower than everyone but Kindl, who plays significantly fewer minutes)
It is only 81 games total in the NHL, but he was thrown in the deep end as a rookie and handled himself admirably (think Kindl or Smith for examples of how else it could've gone). He played big minutes and played all roles on the ice. The question is obviously how much will he improve, but I'd be surprised if he took any steps backwards.
A bit off topic...
DD didn't get to spend any time with Lids - unlike Ericsson, and Kronwall - he was thrown in full speed ahead, and didn't look outta place one bit.
IMHO - he's our 2nd best Dman, and with Ericsson questionable...Well - Holland better get this kid signed.