Seems to me like we pretty much need to keep all of these guys. They all play important roles on special teams. Basically, what it comes down to, is that we don't necessarily need to cut Richards. We need to make sure he isn't seeing defense snaps and having to cover people.
At this point, I think
Richards (309 ST snaps) probably at least plays out the last year of his rookie contract - hopefully as ST-only - more or less what happened with Tavon Wilson.
If
J. Jones (289 ST snaps) is to have an expanded role at CB in 2018, his ST might be significantly reduced from the 65% -70% that he played the past two seasons down to the 30%-40% that McCourty and Chung have typically played. Note that Butler, Rowe, Gilmore and Logan Ryan (his last couple seasons) were used very sparingly on ST. So, JJ's missing ST snaps will need to be filled by someone.
Bademosi and Bolden (284 and 271 ST snaps, respectively) were the next most-used ST players in 2017, and both are UFA. Those ST snaps will need to be back-filled if either of them leave.
If
King (236 ST snaps) stays healthy for the full 16 games (he missed three games and was limited in another this season due to a hammy issue), he'll likely cover another 60 or 70 snaps than he did in 2017.
If
Marquis Flowers (209 ST snaps) is re-signed (I hope), it seems probable that his role on defense would expand - with a bit of reduction in his ST snaps. It already happened this season. As his defensive role expanded after the BYE week to an average of about 50% of the D-snaps, his ST-snap load was reduced from about 65% to about 35%.
If
Jake Hollister (188 ST snaps) can keep up his very much improved ST work (especially on defending units), it will significantly increase his chances of sticking around on the 2018 53-man roster,
almost regardless how much he improves (or doesn't) on offense. He might even increase his ST snap count which would make up for some of the potential losses.
Ebner played only 172 ST snaps this season, down from 359 in 2016. But then, he was only active for 9 games, so his ST-snaps per game-active remained the same (Ebner missed the first two weeks with a shoulder issue and the final five games on IR with a torn ACL). Him getting back to "normal" will also add back a few missing ST snaps.
Develin and Guy played 168 and 166 ST snaps, respectively. I don't see that changing much either way.
Grissom played 153 ST snaps in only 9 games, so his per-game ST usage was just below that of Ebner's. It's what's kept him around. At a mere $720k, I'd expect that he plays out the final year of his rookie contract - on ST - especially considering how easy it's been to slide him back to the PS when the Pats need to sign another guy in an emergency (think, "Ventrone").
Slater (126 ST snaps) missed 7 games and was limited in at least two others with a hammy issue this season that had dogged him since Camp. On a per-game basis, his ST-snap counts were down, too. He turns 33 in September, and retirement begins to seem like a fairly real possibility. If that happens, that yet another load of ST-snaps (not to mention leadership) that will need to be replaced.
Grigsby average about 55% of ST snaps for the five games he was with the Pats this season for a total of 79 (and he performed very well). Extrapolating that level of usage over a full 16 games adds back about 175 ST snaps against those that may be lost due to other personnel changes.
After Grigsby, and aside from the OL guys and kicking specialists, it's really just a handful of ST snaps here and there for the rest of the players on the roster.
So, in response to the 2nd part of the Thread Title question, I don't foresee any of these ST-only guys being arbitrarily cut anytime soon.