That's both true and wrong at the same time.
Sure all the big companies that relied on dhcpcd will rewrite it. But still the loss of one opensource project has a major impact on the economy. You mention the part of time saved by the company. Sure, but that goes longer than that.
For instance, in Android, since Android 6, they stopped using dhcpcd and decided to use their own DHCP client. 5 releases later, Android's DHCP client still don't support storing leases (or any feature that has less than 20% usage really). Sure that's just one packet, but the most user-deployed OS in the world has an additional RTT when connecting to WiFi, because of using internal DHCP client rather than a FLOSS-driven one.
Let's do back of the napkin computation: This adds like 0.5s when connecting. I'd say that personnally I'm connecting manually to WiFi (and thus wait for WiFi to connect) maybe once a week. K, worldwide I'd say once a month. There are 3B active Android devices. I'd say mean salary in those 3B is 1USD/h. If my computation is correct ( ((3*1000*1000*1000)*0.5*12)/3600 ), that makes a society cost of Android NOT using dhcpcd of 5M$ per year.
Now, let's go to the mirror successful part of dhcpcd, still at Google. Chromebooks are using dhcpcd as their DHCP client. Considering what happened on Android, I'll assume that if Chromebooks weren't using dhcpcd, they wouldn't use leases either. There are maybe 100M Chromebooks worldwide, but they are mostly centered in the US where salary is higher, but Chromebooks are mostly for students, so let's make it 5USD/h. But on a Chromebook you connect "manually" to WiFi every day (every time you open your laptop pretty much). That means that the existence of dhcpcd is a gain for society of 25M$ per year ( ( ((100*1000*1000)*0.5*365)/3600)*5 ).
So, yes, if nobody picks up dhcpcd maintenance, companies will have no problem carrying on. It doesn't mean that we, as a society wouldn't have lost a lot.
PS: I'm definitely not trying to put a price on Roy Marple's life. But if someone would try, it would be incredibly high.