My mom has has a 2004 xc70 I found for her, very well maintained, low miles for this era ( 149k ) , she doesn't put many miles yearly ( less than 500 ) but I recently
noticed a pull on wheel to the right, and local shop said a broken coil spring .... it is unsafe to drive for any amount of miles until repair ?
Also, should I only consider replacing both L & R when ready for replacing/repair ?

 

take a look - if its just the very end of the coil (like last 2-3 inches) you are probably safe to drive over to get the repair, but given its pulling, you have an alignment issue which will upset the handling in an emergency. Generally you should always do front struts/springs in pairs to maintain steering, plus if one spring broke - how long before the other spring goes? At 150K miles, it may be just time to do both the front struts/springs and spring seats and be good for another 100K miles. Since you need to do the springs, you may want to shop around to see if anybody sells a front strut kit where the struts come pre-assembled including the springs (not sure if they are available for the XCs )