Can we still play Retribution in Overwatch?

No, like the other annual game modes, this can only be played during the time of year that it is available

Or when the Overwatch team brings it back for a special event

Adding to information from @SPYBUG96 and @Powerlord for a more complete answer. The Archives: Retribution game mode is available each year during the following events:

• Archives - All Archives game modes are available for the full event period (3 weeks)
  • includes Uprising, Retribution, Storm Rising storylines
  • includes Story and All Heroes modes
  • includes Normal, Hard, Expert, Legendary modes
  • includes all related achievements
  • includes option to purchase items with coins from any Archives storyline
• Anniversary - Some Archives games modes are available on some random days during the full event period (3 weeks)
  • could be any of the above storylines
  • could be Story or All Heroes modes (but seems to be usually Story mode)
  • includes Normal, Hard, Expert, Legendary modes
  • includes achievements for the versions that are randomly selected for some random days during the event
  • includes option to purchase items with coins from any Archives storyline

If you want to play Retribution for sure, wait for the Archives event each year. Otherwise you'll have to get lucky during Anniversary for it to randomly cycle (on a daily basis) to the version of Retribution you want.