I'm currently watching the Borg Collection on DVD and noting how many continuity mistakes are made after the first two excellent encounters with them (being Q Who? and The Best of Both Worlds). I Borg was interesting but should have been a one-off, while Descent was a dud. The Voyager episodes were awful - Seven of Nine was introduced to try and boost the show's flagging ratings and the Borg were really watered down. Voyager should have had no chance. Add bad acting; dull characters (always thought only the Doctor and Tom Paris were interesting) and poor dialogue to warped continuity, and you have a tanking show. Regeneration in Enterprise was well done but toyed with continuity. Oh well.
Perhaps one day in a special one-shot Immortus will reveal what happened and what was just wishful thinking. Three seasons of Next Generation and four of Deep Space Nine, methinks.