A Dead Certainty
by Kegler

Ten of the answers must be modified in order to fit into the diagram. It's inevitable that solvers will deduce the two-word phrase those alterations suggest. Answers include five proper nouns.

Across 1 Car rattled; it backed up crazily at first, confusing cleric in northern region (2 wds) 7 Thus, pet returns for Mexican food 10 Trademark protects her measure of heat 12 Favor other holdings for type of IRA 14 Expand about spiritual guide 15 Desert the French way 16 Operating system from Los Angeles in part of Asia? 17 Greeting to continue involving Yoko getting crazier (2 wds) 18 One getting married, surprisingly, in cafe 21 Tom nearly follows a large singer 23 Regarding barrier, one might take this? 24 Unpleasant person, one with title, returning after starting to cry 26 An insane groan disturbed those in the 90's 28 Gets outscored in close series 30 Obliterate half of arch, forming a ring 32 Cathy crashed fancy boat 33 Overgrown, like some Presidents? 35 Strong desire to study “Weird Science” following award 36 Tailless ermine in portico 37 Starts to visualize extremely large developments taking grassland 38 Disparage first of patrons to drink noisily 40 It's part of the foot, Chief 41 I almost did, returning to one with no sense... 42 ...and not nearly the direction 43 In a deliberately obscure way, I call ill type “disoriented”

Down 2 Hears cuckoo birds 3 Start chewing toffee (2 wds) 4 I am getting older making a picture 5 Handgun is fishing equipment? 6 Hear flub earlier in a poem 7 Old Mexican octet milling around lady 8 Rachel's confused man 9 Witnessed part of play in audition 10 Riotously, Greek character starting to laugh, wearing ballet outfit; lousy, lousy 11 Credit fool with cape for lack of dignity 13 Rewinds half of videos; in one, draws goddesses 19 Cutting star running back 20 Doctor O. on “Sunset” features people of mixed heritage 22 Transient starting to notice one empty net surrounding each man 25 One lad excitedly took interest? 26 Disreputable cur also related to kissing 27 Receive every other sign, shoe or gift 29 Good man with urge to sew 30 Frau Elsa harbors “Clan of the Cave Bear” author's family 31 Stony drunk greeting club's leader 34 Two commanding officers have a drink 35 Hot spot for leaderless group of witches 38 That female tennis player doesn't start 39 Official is awake around start of match

Solution