Yes, but only for external contracts. External market jobs are backwards compatible. However, you will not see new DLC jobs added after 1.43.
To get your safe download:
If you own the game on Steam (the standard for 99% of players), you don't "download" a separate file. You . Steam will automatically downgrade your game files to 1.43.
Here is why:
However, if you are a with 50+ mods that break every time SCS releases a new patch, the ETS 2 1.43 download is your lifeboat. It represents a golden era of mod stability before SCS began aggressively updating the engine for the upcoming "Heart of Russia" and "West Balkans" DLCs.
Simply go back to Steam → Properties → Betas → Select "None – Opt out of all beta programs." Steam will redownload the latest version. Your 1.43 saves will likely not work on the latest version, so back them up first.