I haven't researched the other leagues and there might be a coach who was able to turn it around after 8 seasons, but it seems to me that would be unlikely.
I was wrong and there is a head coach who took twelve seasons before getting above 0.500, Minnesota-Duluth's Coach Sandelin.
I've now finished compiling the cumulative records for 389 head coaching stints that lasted more then a single season at all current or former DI schools since WWII (with a few starting before the war). Of those 389 instances, 167 coached for at least 8 seasons, and of those 57 had losing records and 8 didn't return for a ninth season. With Coaches Gendron (RIP) and Cavanaugh among the group of 49 I looked at the remaining 47 and to my surprise I found that 7, about 15%, went on to have a winning cumulative record and 1 is currently at 0.500. I next took a closer look at the 8 coaches and most had some success in both the regular and post season during their first seven seasons. The most successful has arguably been Scott Sandelin, but Ted Donato and Frank Serratore are also in that mix, with Doug Ross also a winner before he stepped down. Here are what each did their first eight and successive seasons:
[TABLE="width: 829"]
[TR]
[TD="class: xl65, colspan: 2"]
Scott Sandelin, UMD, 21 seasons, cumulative 0.545%[/TD]
[/TR]
[TR]
[TD]
First 8[/TD]
[TD]
2 winning seasons (0.583, 0.667), 2 league semifinals, 1 FF[/TD]
[/TR]
[TR]
[TD]
Next 13[/TD]
[TD]
11 winning seasons, 7 league semifinals, 4 championship games, 3 titles, 9 NCAAs, 5 FFS, 4 championship games, 3 titles[/TD]
[/TR]
[TR]
[TD="class: xl65, colspan: 2"]
Ted Donato, Harvard, 16 seasons, cumulative 0.530%[/TD]
[/TR]
[TR]
[TD]
First 8[/TD]
[TD]
4 winning seasons (0.662, 0.629, 0.559, 0.544), 4 championship games, 1 title, 2 NCAAs[/TD]
[/TR]
[TR]
[TD]
Next 8[/TD]
[TD]
6 winning seasons, 5 league semifinals, 3 championship games, 2 titles, 4 NCAAs, 1 FF[/TD]
[/TR]
[TR]
[TD="class: xl65, colspan: 2"]
Frank Serratore, AFA, 24 seasons, cumulative 0.524%[/TD]
[/TR]
[TR]
[TD]
First 8[/TD]
[TD]
1 winning (0.513), one 0.500 season, 4 league semifinals[/TD]
[/TR]
[TR]
[TD]
Next 16[/TD]
[TD]
12 winning seasons, 2 regular season titles, 9 league semifinals, 7 championship games, 7 titles, 7 NCAAs[/TD]
[/TR]
[TR]
[TD="class: xl65, colspan: 2"]
Doug Ross, UAH, 22 seasons, cumulative 0.590%[/TD]
[/TR]
[TR]
[TD]
First 8[/TD]
[TD]
5 winning seasons (0.518, 0.667, 0.596, 0.611, 0.554), 1 DII Frozen Four championship game[/TD]
[/TR]
[TR]
[TD]
Next 14[/TD]
[TD]
11 winning seasons, 2 regular season titles, 1 tournament title, 3 DII Frozen Four championship games, 2 titles[/TD]
[/TR]
[/TABLE]
Looking at Coaches Donato's and Ross' success those first eight seasons it's a bit surprising both had losing records. Then there are the 3 coaches who got their cumulative winning percentage above 0.500, but never did much before or after their eighth season:
[TABLE="width: 829"]
[TR]
[TD="class: xl65, colspan: 2"]
Craig Dahl, SCSU, 18 seasons, cumulative 0.521%[/TD]
[/TR]
[TR]
[TD]
First 8[/TD]
[TD]
2 winning seasons, 1 NCAA[/TD]
[/TR]
[TR]
[TD]
Next 10[/TD]
[TD]
7 winning seasons, 5 league semifinals, 1 tournament title, 4 NCAAs[/TD]
[/TR]
[TR]
[TD="class: xl65, colspan: 2"]
John Markell, OSU, 16 seasons, cumulative 0.511%[/TD]
[/TR]
[TR]
[TD]
First 8[/TD]
[TD]
3 winning seasons (0.667, 0.561, 0.550), 3 league semifinals, 1 championship game, 2 NCAAs, 1 FF[/TD]
[/TR]
[TR]
[TD]
Next 8[/TD]
[TD]
4 winning seasons, 3 league semifinals, 2 championship games, 1 title, 4 NCAAs[/TD]
[/TR]
[TR]
[TD="class: xl65, colspan: 2"]
James Fullerton, Brown, 15 seasons, cumulative 0.511%[/TD]
[/TR]
[TR]
[TD]
First 8[/TD]
[TD]
3 winning season (0.526, 0.522, 0.688)[/TD]
[/TR]
[TR]
[TD]
Next 7[/TD]
[TD]
6 winning seasons, 2 league semifinals, 1 championship game, 1 FF[/TD]
[/TR]
[/TABLE]
And finally there is the coach currently at 0.500:
[TABLE="width: 829"]
[TR]
[TD="class: xl65, colspan: 2"]
Derek Schooley, RMU, 17 seasons, cumulative 0.500%[/TD]
[/TR]
[TR]
[TD]
First 8[/TD]
[TD]
1 winning (0.586) and 2 0.500 seasons, 5 league semifinals, 2 championship games[/TD]
[/TR]
[TR]
[TD]
Next 9[/TD]
[TD]
6 winning seasons, 3 regular season titles, 6 league semifinals, 4 championship games, 1 title, 1 NCAA[/TD]
[/TR]
[/TABLE]
So, there was a chance, however unlikely, that Coach Gendron could have turned it around and gone on to have a cumulative winning record. However, even if he had I don't think he would have been in the first group. Nor do I think Coach Cavanaugh will end up in the first group.
Sean