I have had hosts for years, first at Venetian, then at Mandalay Bay when she moved over there.
Based on my experiences, here is what I think:
(1) When your new host said "I will evaluate both play", he definitely means both you and your fiance. In the future, you can ask your host to book your room as a "share with", meaning both occupants' play is evaluated together to achieve the level of play he/she is expecting for comps.
(2) Your specific host does not need to be working on the day you check out. Instead of asking an unknown host to evaluate your play at the end of your stay for additional comps such as restaurant charges on your room bill, ask the host desk/VIP lounge/front desk to leave your account "OPEN" when you check out. They will then understand that you want your host to evaluate your play when he/she returns to work that week. Nothing will be charged to your credit card, then, until your host has had a look at it.
(3) Your upfront free night coupons are generated by the Casino Marketing department, not the hosts themselves. However, comps are comps in terms of rooms. In other words, your future offers from marketing are dependent on your previous stay's play. As my host once said, "you wouldn't be invited back" if you didn't meet the expected play on your last trip. It isn't a "scare tactic" or any kind of a threat, since the host is only matching what the marketing department is giving you upfront. It only becomes problematic if the host has taken a chance and "overcomped" you, as in giving you a suite upgrade in advance of your stay.
(4) Even if you continue to receive free night coupons in the mail, continue to always book those marketing department coupons through your host, not the phone number listed on the coupons. Your host does indeed get credit for you play, as his salary/bonuses are based on bringing in players and retaining them.
(5) If you find a good host, stay with them. We once were lured into trying out a new host at a casino where we've never played ---at the Cosmo. It didn't work out well for us. He comped us upfront, basically "status matching" our player's card level at Venetian. We ended up hating the casino for many reasons and so gambled very little in our three night stay. Well, he emailed me and called me repeatedly during that three night stay, insisting he see "more play" from me in the casino immediately. He had "overcomped" me upfront, always a risky thing for a host to do for a new, unknown player, and he "lost." It happens.
(6) There are different comp levels, and you work your way up to levels that include free rides to/from McCarran or food comps upfront. But, I would never ever gamble more than is comfortable for the sake of saving the $12 cab fare to TI or wherever.