Yes, RUT950 should do all of that just fine. It has a failover functionality that will toggle between SIMs if there's a loss of signal, data limit, reaching SMS limit and even more.
All the switching conditions are available for review here: https://wiki.teltonika-networks.com/view/RUT950_Mobile#SIM_Switching
Also, you will be able to switch between interfaces, so in case your operator dies on the mobile side - you can switch to Wired WAN or WiFi.
If you want to reach even more stability - I highly recommend RUTX12, which as a product is performing even better, because of its better memory and CPU, but the main feature of RUTX12 is two active modems. With two modems you will be able to run both SIM cards at the same time without switching between them, so you should see almost unnoticeable failover functionality as it doesn't require time to switch into another modem (that is already working).
In any case, I really recommend that you read our wiki, as you will find most of this information there:
Hope this helps.