Somehow I feel the sunlight vulnerability is a bit of a cop-out, a older-E approach to class balance not appropriate to 4E. Mostly because of the "instantly destroyed" part.
Death is one of the issues not very well handled in 4E, IMHO. Although it is quite rare on the whole, it is rather devastating when it eventually occurs. It becomes a burden for players as well as the group as a whole, both in and out of the game. In game, resurrection is costly and (might be) hard to come by, and the character is penalized afterwards (for being alive). Out of game, the party becomes weaker (short and long term) and must (or might) take measures that deviate from the story or quest at hand, thus (possibly) devaluating the experience of the game session. Finally, the dead characters player is forced to idly follow the game from the sidelines unless given opportunity to play some other, generally less appealing, companion character or such. All in all, this causes more problems than it solves, mainly because there is little choice in the matter for the players in question.
Therefore I'd suggest adding in a clause derived from Terry Pratchetts approach to
vampirism and sunlight in the Discworld, which seems fitting to me. I'll highlight the part in question:
Discworld vampires can survive in sunlight, provided they wear heavy clothes and broad-brimmed hats. As before, some vampires believe conditioning would reduce their vulnerability to the sun. When exposed to any strong light source (such as a camera flash) they will be immediately reduced to ashes, but require merely a drop of blood to recorporate. Many Black Ribboners carry "the kit", a dustpan, brush, small phial of animal blood and explanatory card ("Help,I have crumbled and I can't get up. Please sweep me into a heap and crush vial.I am a Black Ribboner and will not harm you") asking bystanders for assistance in reviving them; Otto Chriek carries his own self-revival kit (a extra fragile glass phial of blood that breaks upon impact) for automatic recorporation, since his salamander-powered camera flashes have a tendency to turn him to ashes.
Emphasis mine. Downplaying the comedic aspect, one could easily translate this into 4E terms:
A vampire character reduced below 1 hit points from radiant damage due to being exposed to direct sunlight is instantly turned into a pile of ash, and is effectively removed from play. An ally adjacent to the pile of ash can spend a healing surge as a standard action, where upon the vampire character returns to play with 1 hit point, lying prone where the ash once was. A vampire character returns to play on it's own after 6 hours.
Now, there are some apparently obvious issues here (ex. what if there's a strong wind?) and some room for exploitation (ex. a vampire turned to ash transported in a bag of holding past enemy lines), but I kind of like the idea of such scenarios and the dramatic opportunities they imply. What I hope this would achieve, though, is to add incentive for vampire players to risk fighting in sunlit areas and not feel gimped because of the tone and environmental aspects of the story. Hell, I'd recommend doubling the radiant damage dealt by sunlight since it'd be less of a burden and more of a gamble with my suggestion.
Thoughts on this?