There will be a place for both for some time. If you look back to when digital surpassed film, there were some early adopters of digital for some uses, but for quite a while, images from digital didn't meet the quality people had come to expect from film. As digital quality improved, more people made the switch. Now, digital is king and film, though still used, has become a niche market.
Mirrorless will likely go the same way. There are some early adopters, but mirrorless systems don't yet have all the features that people have come to expect from their DSLRs. Eventually those features will accumulate and reach a tipping point, and DSLRs will be a niche market. When that day will come is unknown, but you have to decide what features are critical for your work and what gear meets those needs. Future resale value should play no part in this decision because everything you buy will be worth less as time passes; if that's a criterion, then you'll never buy any gear. Your 35L II could pay for itself may times over long before you need to consider resale value. And at that point, it will be fully depreciated and anything you get for it when selling will be a bonus.