I saw everywhere that the reason SK is dead because prize boxes blah blah, Lockdown toxicity blah blah, but everybody think it is OOO's fault. Maybe it isn't OOO, but Sega?
Anyways, it's up to either one of them to continue development of Spiral Knights. Either they keep releasing new content as small updates to conform with other games (think Alpha/Beta games in live development) or abandon the game completely, focus on other games (i.e. Puzzle Pirates, one of OOO'S games) and forget about us, the community (for example the standalone paid games released many years ago). Sega must to decide if they want to continue developing/partnering with OOO so we don't complain how this game is dead. Also, some more frequent updates with 1 new thing every ex. 2 months won't even hurt, especially enough to keep people from complaining how the game is dead right now.
Alternatively, when they will finally give up on prize boxes, then...nothing else, but post a note in Announcements that Spiral Knights is shutting down irreversibly. Not to suggest OOO on killing SK, but they might soon run out of known gemstones to release prize boxes for and people don't like same prize boxes all over again, especially when they hold same content as they knew.
So, maybe it isn't Three Rings' fault that Spiral Knights is dead, but Sega is behind this game nearing to f2p abandonware* state?
*Abandonware - a game that was abandoned by its devs. No more updates will ever come to abandonware, and (probably) is free to download.
You're saying it like three rings still exists as a separate entity. My current understanding is that three rings is no longer a separate company, but was merged into Sega Networks LLC with other game studios. The former CEO is supposedly no longer (cleaver posted a note here - http://banghowdy.com/support/ ). Their public linkedin corresponds with this information. It also explains why Rise of Knights even happened (Sega Networks LLC is a mobile app division of Sega).