When you're done building the minimum viable product. You're not done, his value is not used up. You've done only a fraction of the work involved with building a company. The real hard work now begins. I've done this a few times, so i'm talking from experience here. Build it, and they will come... is a fallacy.
You'll need him to get in the door. Yeah, getting in the door of customers is hard, even if you have a product they want/need. You'll need him to help you gain their trust (you're not selling steak knives here, you're selling enterprise software!). High value sales means building a relationship, understanding the process of having clear goals with each engagement, demonstrating the value, integrating feedback, etc. You need an expert who understands sales, and the industry. If he's a consultant, presumably he has this.
You MIGHT be able to do this yourself, but even if you eventually succeed you're probably going to fail a lot before you get it. If he already has the skill set, and he already has the network, and he already has the relationships. He's bringing A LOT to the table. This isn't you working for him, this isn't you working for fee. This is adding his complementary skill set to your own, and building a company.
The one last thing I think every engineer who wants to break out and do their own thing should know. You can outsource product development (not saying you should, just saying you can) but you CAN NOT outsource sales. There are consultants who will help you, there are distributors, but none of that can completely replace having your own dedicated sales/marketing staff. They're augmentations. Building a company is not just having a product, it's having a market, it's knowing the market, and it's having a strategy to penetrate the market. The product is just a part of the company.
I recently quit my job to bootstrap a SaaS. I spend 60 hours working on it a week, and 55 of those hours i'm doing something that isn't coding. I REALLY want to just write some code, but that's not the most important part... not right now at least.
My advice is don't underestimate the value an industry expert who knows sales can bring to the table, and try to be realistic about what your skill set is.