Many outside observers back in the day expected the FSLN to win the election. What would be different if they did? I'm running a geopolitical simulator set in 1990 and, after I decided on 8 out of 10 chance the FSLN would lose as they did in real life, the random number generator I use to determine outcomes decided they would win.
Pro-Sandinista sources argue that much of the FSLN's defeat was due to the US threatening to perpetuate sanctions and the Contra war if the electorate made the "wrong" decision. On the other hand, the FSLN in subsequent years (after losing 1990) built up ties with the Church, former Contras, and generally projected a more moderate image. I'd assume the FSLN winning 1990 would still continue the pro-market reforms it had been undertaking since the late 80s in an effort to improve the economy and, with the "fall of Communism," convince the US to at least tolerate a Sandinista-ruled Nicaragua.