I certainly remember seeing Will Lee's (and later Northern Calloway's) obituaries in the newspaper at the time they occurred. By 1982 I was in high school and I had not "regularly" watched Sesame Street in several years, although I would tune in for a moment here and there sometimes and check it out. I do remember tuning in after his passing and still seeing Mr. Hooper in the store, but I couldn't tell you an exact date.
Oddly, one of the days I did tune in for a moment (this was a few years later) was when Big Bird was telling a kid who'd never met Mr. Hooper about him. He'd tell a story and ask the kid "do you remember him now?" and the kid explained that no, he can't "remember" him per se because he never knew him, but at least now he knows a little about him. This ended up being part of the Sesame Street Unpaved series.
After Will Lee passed away, I remember reading about how they were going to acknowledge his death on the show and I thought it was odd since it was almost a year after his actual passing. But at the time, I didn't understand how the production cycles worked and it didn't occur to me that there was a big backlog of taped episodes already in the can, and then they would go into reruns.
I meant to tune in that day but ultimately I forgot, so I never saw #1839 until Noggin ran it years later.