I searched a bit and nothing points that the strikes will be extended. The services are rather cooperative and informative.
Here's a couple of sites you can look out for developments:
For the Rer, which is normally all you need. You'll have to take the Rer B till St Michel Notre Dame, and then the Rer C till Velizy.
http://www.transilien.com/web/site/accueil/etat-trafic
General info on the strikes:
http://www.abcdtrain.com/
And the classic ratp info which is more detailed than I hoped it would be:
http://www.ratp.fr/
Anyway I wouldn't worry, I'm pretty sure there won't be any problems tomorrow. You can't immobilize a city for more than 1 day.
I'm more worried about me since I have to walk from Montmartre to the center of Paris on foot with a 7 kilo instrument on my back today...and I'm afraid not many people will be present at the concert because of the problems.
Anyway, I couldn't think of any worthy alternatives...either a taxi, that will cost you one month's salary of your new job if you get it, or a Velib (rent-a-bicycle)
.
Good luck!