So your game's been away a while, in and out of character. Circumstances like players coming and going encourage you not to pick up exactly where you left off.
Not enough to reboot but enough to consider what's happened and what to change about the format as a result.
(Inspired in no small part by the DC Comics reboot/relaunch/rebrand/rethink/remake thing, but also by a page of Buffy Season 9 Issue 1 online for Joss Whedon's birthday. Happy birthday Mr. J!)
So how has the status quo changed by and for the PCs and major NPCs?
How long has it been? Last time DC rebooted itself it went "one year later" to excuse various changes to all sorts of titles. TV series may or may not acknowledge the gaps between series, often depending on whether they ended with a cliffhanger last time. The Buffyverse is always quiet during the summer, but things may still happen before the first episode of the new season kickstarts the year's mayhem.
Who's around, who's not? This can reflect changes around the table, but applies to NPCs as well. Season three of SteveD's The Night Watch started with the Watchers' much-loved invigilator replaced by a much sterner instructor. A new academic year (in and out of character) brought new PCs and NPCs to The Watch House as well.
Has a PC powered up or down or changed in some other significant way? If so, how and why? If there was a major change at the end of the last adventure, how is that being dealt with?
Are two nations over there now at war or making peace, have the stars fallen from the sky, has Atlantis risen, did someone behead Vecna again?
Depending on how you left the game, this could be a slight streamlining of the setting, a "back to basics" issue 1 relaunch, a "nothing will ever be the same again!" development where things may or may not ever be the same again depending on the players' preferences, a post-apocalypse nightmare where the PCs were around for the apocalypse, a the-PCs-ascended-to-godhood-what-now? emergency depowering, a Next Generation...