In the end, Sega only has themselves to blame for their falures. EA didn't force the Sega CD onto consumers who didn't want it, nor did they speedily release the Saturn when neither retailers nor consumers were prepared for it.
I don't see Sega becoming "the next 3DO", because 3DO wasn't as big an icon in the industry as Sega, and Sega does have numerous stellar franchises to fall back on like VF, Shenmue, Jet Set/Grind, Super Monkey Ball, and Yakuza. In some cases, like SMB and VF, they sell very well and can keep the company active. Sega's got a nice mix of IPs for hardcore and casual gamers right now, so they can please both markets and keep themselves active.