I was supposed to travel to Paris from Barcelona on 7th June via the 9:25 train. But due to the France railway strike, all the trains on 7th June are cancelled except the one at 1:25 pm. The problem is, I will reach Paris by 8pm, loosing almost half a day of my originally planned 1.5 days' excursions. I am on a tight schedule here, which has made me consider the option of flying via Vueling air. Any ideas on how reliable (delays etc), and safe the airline is? Should I consider this alternative, as I will gain almost half a day more in Paris?
Vueling is just fine. All EU-based airlines are generally safe and Vueling appears to be among the most punctual.
It's a low-cost airline so you can expect a bare-bones service compared to long-haul flights on legacy airlines (for short-haul flights, the difference is not large). Low-cost airlines tend to use different terminals or different airports and to enforce luggage rule very strictly, to name a few differences.
Going by plane will be the fastest.
A cheaper option is to use a bus. It will cost you around 70€ by Eurolines. Good thing is you'll arrive inside Paris, not at an airport. But you'll have to sit in a bus for about 15 hours.
As for your other question (how to go from Paris to the airport when the trains are on strike) there is a bus service. Google "navette" and the name of the airport. Expect the price to be horrendous though. Here is an example.