I too watched these episodes again this weekend. I didn't think they were that bad, but maybe that is because I really like Dana Delaney. And I didn't think the "lack of chemistry" between her and TS was THAT bad. He really didn't have chemistry with any of the women he would grab and kiss in the show (Andrea Marcovicci in either of her guest roles, Cynthia Sykes in "The Kona Winds," Sharon Stone as the twins, etc.) except with Marta Dubois as Michelle (and none of us like that anyway . . . .). Because I found Dana's character to be more likeable than the other females recited above, I could better understand TM's attraction, and I thought the hesitation of their kissing was more touching and convincing that his "snatch and grab" kissing with the other women.
I agree that the proposal was WAY off base. I realize that there is frequently a very strong bond when a male and female go through a dangerous situation together (see "Speed" with Keanu Reeves and Sandra Bullock). But this wasn't that intense a situation, i.e., it didn't take place within 12 hours. I think an invitation to spend some time with him in Hawaii would have been much more believable. The marriage idea seemed to be the writers' pushing too much for an ending for the show -- that's as close as MPI came to jumping the shark, in my opinion.
As for getting involved with someone plagiarizing Robin Masters, he had sort of finished his Robin chore when he served her with the papers. What happened thereafter wasn't really his choice. The murder of the comedienne he met on the airplane had nothing to do with his errand for Robin, and that's what got TM and this Cynthia involved together. It seemed that everything just threw them together when that issue came up, and I can't see his just abandoning her at that point, once she had, admittedly, involved herself in his situation. And actually she was helping him, risking her life to help him solve that murder.
Also contributing to the unreality of the marriage proposal and the "dump" at the airport -- if they were going back to Hawaii together, wouldn't he have stayed with her and wouldn't they have gone to the airport together? His being there waiting for her didn't make sense to me. Once a couple is a "couple" and "together," they don't go to the airport separately. Wouldn't he have, basically, changed location to be staying with her? Wouldn't they have spent the night together before leaving for Hawaii the next day? And consequently leaving for the airport together from her place? Again, the proposal and the jilting was a "deus ex machina" (Google that if you don't know what it means) plot twist that was illogical for the episode, the show, the series, the Magnum character. Instead of miraculously solving a problem, it unnecessarily created one that then suddenly had to make an about face. Since that wasn't the crux of the plot, I won't call it a jumping the shark for the two-part episodes, but it was darned close.
Now the final episode of "Resolutions" was the true "deus ex machina."