It's not a binary issue, though. There's plenty of variety in 4e fans. There will be some that enjoy 4e's feel and gameplay without being wedded to the mechanics. Folks like me, who like having the DM tools, wizards with at-will spells, fighters with options, non-magical healing, the PoL setting, and granular combat with clear rules for using maps and minis. The 5e hurdle is much lower for these folks. Then are those who have absolutely no interest in playing with 5e's ruleset, who want to keep playing using the 4e rules. But they want support. They like using published adventures. If WotC can release decent adventures easily converted to 4e rules, then this group is a possible market. Then there are those who want absolutely nothing to do with 5e, and in fact, really want nothing to do anymore with WotC. Maybe they'll only hold on to a DDI subscription as long as the 4e tools are available. Maybe they won't even want to do that. This group is essentially lost to WotC. The best they can hopeful are occasional 4e PDF purchases. Maybe an edition-neutral PoL book, if they're really into the setting.
It's pure speculation, but I suspect the first two groups combined will be larger than the third.