I totally agree with the OP. I've been bitten by this "feature" on several partner award tickets, which -- on popular routes -- by necessity have to be booked nearly a year out.

I have found out on my own:

In 2009, that British Airways had decided to stop flying to/from Dublin, leaving my spousal unit and I potentially stranded without a Dublin-LHR flight leg on our return to Seattle after they unilaterally cancelled it;

In 2013, that Alaska Airlines had a schedule change SEA-SFO that made a connection on an Air France flight to CDG almost impossibly tight;

And one or two others that do not come to mind immediately.

But in all these cases, I was not notified by AS. I had to proactively and regularly check my flight reservations with both AS and the partner website and make multiple calls to straighten out the changes.

Now, I put up with this because I really like the flexibility of award redemptions on AS and its eclectic group of partners. But I don't like having to figure out myself that something has changed. (That said, I'm doing that all the time on AS-only paid tickets during each quarter's schedule change-fest, when flight segments simply disappear from the mobile app and become inaccessible on the website.)

There must be a better way.