D11/D13 Tandem Pump and DEF pump - life expectancy/when to replace?

I've got a 2012 D11, 925k miles and 35k engine hours. Trying to get another year out of this truck and I do my best to avoid breakdowns so I like to replace things as preventative maintenance. The tandem pump and DEF pump are original to the truck as far as I know. Do they give any warning signs before giving up? like occasional weak DEF or Fuel pressure codes? or do they just fail all at once? Any idea how long these typically last?

anything worth testing such as fuel pressure or def doser line pressure that might indicate they are getting weak?

Thanks!