Diesel emissions will improve to meet requirements, or requirements will be adjusted to allow diesels to be utilized. There were lots of missteps along the way with gasoline engines as well, and they have been regulated with emission standards far longer.
As for the future, it's hard to predict. In the 1800's, it was predicted that solar energy would replace coal fired generation by 1900. Predictions were based on both photovoltaic solar cells which were around 1 percent efficiency at the time, and power generation using mirrors to direct the energy to steam generators. Sound familiar.
Unfortunately, I don't see any battery breakthroughs out there currently that show promise for vehicles requiring any significant power such as RV's, semi trucks etc. Batteries are an area where the hype is really getting out there in regards to service life etc. For decades, the standard for useable cycle life used to be 80 percent or more of original battery capacity. Now there isn't really any standard. In looking over the data for the Chevy Bolt for instance, it appears they use 60 percent of original capacity when talking cycle life. In well over 100 years battery improvements have been a slow incremental process.
Time will tell, but my thoughts are that something more along the lines of fuel cells will be the replacement for Diesel if and when diesel has to be replaced.
