Are there enough other paths through the game to complete the base campaign of Shadowrun Returns without ever using Decking?
There are some mandatory missions that require a decker.
On these missions an NPC decker will either automatically accompany you, or one will become available when selecting your team.
No. There are some missions that require a decker (either you or someone else). And otherwise, you will miss out on a great deal of money and other things without a decker. However, there are some very good combat deckers that are good at fighting also, so check them out as well. Especially check out the Nebilim (I think it was) network and see if you find any good ones in there, depending on how far into the game you are.