I'll make a cider with Lalvin EC-1118, but I want to know if there's a chance to harvest the yeast cake after fermentation. Normally, I don't have problems reusing ale yeast, but this champagne yeast I don't have clue if the wash process is the same.
I have not made any cider yet, but there should be no problem in reusing the yeast with one exception:
If you have so much fermentables that the cider would finish sweet, you have killed the yeast, so that the cake only contains dead yeast (I am thinking of having a potential alcohol level that is higher than what the yeast can tolerate). Most yeasts can tolerate up to 12%, but I have seen yeasts up to 18% and heard of some above that. (Your yeast tolerates up to 18% according to http://www.lalvinyeast.com/strains.asp )
The downside of reusing the yeast of a wine, mead or cider might be that the yeast is getting stressed by the alcohol.
I suggest that you simply try it and see if you get good results (which is what matters most). If the fermentation doesn't start in a timely fashion you can always pitch some fresh yeast...