This was a rare Monday puzzle wherein I understood the theme while solving, and used it to help me fill in theme answers quickly, although, I admit, I wasn't positive about the spelling of DOSVIDANIYA (24D: "Farewell, Vladimir!"). Even without that, though, I felt it played a little tougher than Mondays sometimes do. Actually, I finished with an error "BABe" for BABY (25D: Infant). Such are the perils of trying to solve for time. The squares get filled in, and I do not double-check them. My grandmother had a trivet on her wall that said "The hurrier I go, the behinder I get." I should, perhaps, keep that in mind more often. Lost at least 30 seconds looking for the mistake. Sheesh!
I enjoyed the theme well enough, and I loved the bluntness of the revealer clue - 34A: This puzzle's theme (GOODBYE). Sometimes it doesn't take much to amuse me. At first I was a little bothered by ACDUCTS (22A: They connect cooling units to rooms, in brief), even though it's perfectly fine fill (sometimes it doesn't take much to bother me, either…), but I liked it better when the next answer was BMOVIE (25A: Unmemorable low-budget film). Somehow, having all three single letters (A, B & C) seems better than just having one or two. Crazy? Probably.
I wish the clue for ONEMAN (20A: Kind of band) were "What can I do, I'm only ____?," but I guess that's another one I'll have to jot down in my virtual notepad.
Some of the usual stuff - EMIR, URSA, UTIL, ERIE, and a blast from the crosswordese past with OREL (16A: Pitcher Hershiser), but nothing terribly egregious. Plus, there's some interesting stuff, like LAPIS (1A: ____ lazuli), CHINK (23D: Armor flaw), TENPINS (45A: Bowling game), and DOUBLEDUP (30A: Bent over, as from pain).
A fine Monday.