I suspect Italy or Brazil might have won if it had been hosted elsewhere! Also could not hosting it in 1978 have precipitated an earlier Melvinas crisis with Vidella and the 'Lads' intervening sooner!
What were the other likely hosts? Colombia was awarded 1986 tournament, but couldn't take it due to an eathquake!
Indeed, most probably a victory for Italy or Brazil, maybe the Dutch at a stretch. As to who could have hosted, I believe the only other country to consider a bid had been Mexico, who pulled out after they were awarded the 1970 World Cup, so a different host is required. Since 1958 FIFA had alternated between Europe and the Americas, and by 1978 they were running out of hosts in the Americas who weren't Argentina, having snubbed them as hosts for '58, '62, and '70. If they were to hold it in Europe, the natural choice would have been Spain, who had bid for '66, and withdrew their bid for '74 in return for West Germany's support for '82. Otherwise, perhaps USA (who bid to replace Colombia in '86), or as you say, maybe an early Colombia?
You're incorrect about Colombia not being able to host in 1986 due to an earthquake, by the way, Colombia were unable to host due to financial problems so withdrew in 1982 - Mexico subsequently suffered an earthquake in 1985, which caused some to doubt whether they would be able to host in '86, but the stadia were unaffected.