Assuming that Bush is the Republican nominee or Reagan is actually killed early in his first term:
How would the economy and financial states of the United States develop?
Those are two different scenarios. If the POD is Reagan dies in March of 1981, Bush might be more compelled to honor his predecessor early on. That means the first tax cut goes through easily, perhaps no TERFA, not sure if Bush plays hardball with federal unions (bear in mind Reagan had been head of the SAG at one point and honoring Reagan might well have meant being fair with unions) and getting tough with the USSR albeit not necessarily taking to Up To Eleven by calling them an “Evil Empire.” By his second term, he probably vetoes the 1986 tax cut as going too far, and if one passes, it’s toned down big time.
If Bush gets the nod instead of Reagan in 1980? He’s doing it his way and Reaganomics can go straight to hell. Probably still means a tax cut but not anywhere close to as drastic as how the Reagan era ended (no cutting the top tax bracket from 70% all the way to 28% for one.)