Hope Reiji doesn't dare to call Nagi to her phone, considering sensei has her phone and may take advantage of that.
If Reiji bites the b8 (in case sensei answers and pulls her better Nagi impersonation to lure Reiji) and goes to meet "Nagi", only to find the actual truth... he may end up snapping and may do something that will put him at irreconciliable odds with law enforcers. Iirc, there were 3 things that actually pissed Reiji off or made him act out of his listlessness and be an actual person: Esemori using Chako, Sensei destroying the latter's dream and Gen trying to beat the living shit of Nagi and killing her. If Reiji finds out Sensei is the cause Nagi couldn't contact him and viceversa, sensei may end up knowing Reiji's angel of death persona. And either he'll lash out... or politely say nasty things to sensei for the sake of mere emotional torture.
Lowkey, i want sensei to try, on her increasing desperation and denial of reality, to sell Reiji the idea of why she's so fixated on saving him and why she thinks she loves him and use that first encounter from the Senkou Shoujo one shot (when kid Reiji gave JK Sensei back something she dropped to the floor) as the main excuse on why she thinks they are fated to be together. Even if Reiji proves her why it's a wrong thing to think so.
Considering the thematics of these climax closures, every one of the people Reiji has met again in The Town has wanted to become Yuko in some shape or behavior (Gen, Chako, even though she didn't know her wish was to become the woman who keeps tormenting Reiji), but what if Reiji makes sensei realize she is just being like his mom by doing everything she is doing??
Maybe all this shit would be even beneficial for Reiji and may give him more insight about what he is searching for on his quest for answers so he could face the real Nagi: by realizing Sensei has the same desire Yuko has (not being left behind by people for being a 29yo single woman with a dead end job), but is also doing the same wrong thing Yuko does (isolate Reiji and have him only for herself as a result), he may finally realize what Yuko wanted all this time was to be loved and not left behind for being sexually exploited, AKA, tainted.