The last couple weeks were a dumpster fire for Cruz. The alliance with Kasich, the unprecedented declaration of a running mate when it was mathematically impossible for him to outright take the nomination, dropping out a week after doing that... I don't think voters will buy a return by him. He undercut his outsider status with these idiotic moves and still remains deeply disliked by most prominent Republicans. And it's not like he's all that likable anyway. He literally only got the traction he did due to being the only viable Trump alternative, bolstered by the types of voters who elevated such "successful" candidates as Rick Santorum.
Besides, Cruz is no Reagan. Right-wing pundits basically compare everyone they like to Reagan but seriously, what do they have in common? He's not likable or charismatic (he instead comes off as dry and measured). He's most notable for a staunch refusal to compromise. The party is packed with people who outright hate him (no exaggeration, hate him!). That just.... isn't anything like what appealed to people about Reagan at all.