Heynckes' men overcame Dortmund in Saturday's UEFA Champions League final at Wembley, thanks to a late winner from Arjen Robben.
Lewandowski has won plaudits for his performances this season, particularly his four-goal showing against Real Madrid in the semi-final stage of the same competition, and has been continuously linked with a move away, with Bayern among the front-runners for his signature.
Heynckes had previously been coy on the subject, but suggested deal is in the works and that the Allianz Arena outfit are only waiting on a decision from the Polish striker.
"I'm handing a perfectly functioning team over to my successor (Pep Guardiola)," Heynckes said. 
"From what I know about Bayern, and it's already known that we signed Mario Goetze for the new season and surely Lewandowski won't keep us waiting much longer, and with them we will gain another two top offensive players."
Bayern have spent big to secure both the Bundesliga title and European crown, and can become the first German side to win a league, cup and UEFA Champions League treble if they beat Stuttgart in the DFB-Pokal final on June 1.
Heynckes feels the success they have enjoyed this season has justified their transfer policy and was eager to praise the character of the players brought in.
"We had some risky transfers, like Javi Martinez, with the large transfer fee we paid, not the quality of the player, or (Xherdan) Shaqiri or Dante," he added. 
"But all of the players we brought in were a hit, also character wise. And of course I think that, in the next year, the new Bayern coach will also have to prove that he can continue like this. 
"But surely it's quite possible that, thanks to these specific transfers, there could be a new era happening, in Europe for Bayern Munich."