I would expect the 1DXIII to be in production for several years and to overlap with the R1.

Looking over at the Canon website, the 1DXII, 5DIV, 6D, 6DII, 5DR, and 5DRs are all still listed. This is fairly typical of Canon as they keep older models for a couple of years after the newer model is released.

It all depends on sales, and when inventory/parts run out. But if I were to guess, the 1DXII, 6D, 5DR and 5DRs will be discontinued in 2021. The 5DIV and 6DII in 2022 maybe 2023 on the 5DIV. I suspect the 1DXIII will be given a solid 5-8 year run, so say 2025, which could be when the R1 Mk II is announced, or longer. One of the complaints about EVFs is eye strain for those continuously taking pictures for hours on end, which is one of the target markets of the 1DX series. Also, one bit of speculation I have read is that groups (Reuters, etc) with large EF lens inventories want a professional body and do not want to mess around with adapters. The 1DXIII keeps these groups happy and from switching companies while Canon develops their new RF lens lineup and those groups get ready for a massive purchase when they swap systems (thus, they may put off swapping systems for a long time).

So, no, I do not expect the 1DXIII to go anywhere anytime soon. Having played with it myself, I do not see the reason. Great great camera.