A lot of relatively obscure languages will die out, but no, Spanish and Portuguese won't merge although portuñal will remain widespread in certain areas. 

Nobody knows what is going to happen with languages. From history, many languages died and from present, languages are changing, evolving. Just look at English. There are words that were used in 50's and now they are consider to be "old fashioned". I am sure, you can find shiny examples regarding your native language as well.