The Albert Square legend, played by Pam St Clement, will discover that she is terminally ill within the next few weeks but initially keep the news a secret from her loved ones, according to The Sun.
Sources say that Pat later organises a party at the Queen Vic for her family and friends, which sparks the rumoured return of her sons Simon and David Wicks (Nick Berry and Michael French).
With everyone gathered around, Pat reportedly comes clean over her illness, explaining that she has thrown the party to give those closest to her a chance to celebrate her life.
As the bash continues, Pat apparently slips out quietly and returns home as she feels unwell, before passing away peacefully in bed.
An EastEnders insider told the newspaper: "There was no way bosses wanted Pat to sign off with a grisly death. It was always going to be a dignified farewell in which colleagues and viewers could raise a glass to her."
Ricky and Bianca Butcher (Sid Owen and Patsy Palmer) are also expected to be back for the scenes, which will air at Christmas.
In a separate development, The Sun also claims that show villain Yusef Khan (Ace Bhatti) will be killed off in the soap's upcoming B&B fire storyline - a plot now known to be unrelated to Pat's departure.
All details of storylines and possible returnees for Pat's exit remain unconfirmed by EastEnders bosses.
> Pam St Clement quits EastEnders: 'It's time to hang up Pat's earrings'
> EastEnders Pam St Clement's exit storyline revealed?
> Read more EastEnders spoilers and news
Watch Pat Evans's EastEnders character trail below: