Whether to leave fallen leaves on the lawn or on ivy overwinter mostly depends on how thick the leaves are.

While it is at least partially true that excessive amounts of fallen leaves can smother areas of a lawn when they're left in thick piles all winter, leaving a thinner covering of leaves can actually be an effective method of building soil and supporting a healthy yard. Something to think about for next fall would be to mow over the fallen leaves a few times before they become thick on the lawn. These shredded leaves actually improve the nutrient level of your soil. 

Do you plan to blow them off the lawn and onto the ivy? If you have the ability to blow them off one or the other, why not just blow them into a couple of piles somewhere out of sight? (I realize that may not be possible though.)
Leaving the leaves on ivy also depends on how thick the ivy plants are at ground level and how high up the ivy the pile would be. If your ivy is evergreen, the leaves of the ivy shouldn't be covered because the ivy continues to photosynthesize during the winter. If you do keep the leaf cover, you will need to rake off any heavy wet leaf mass that is there in the spring.
On the other hand, leaving an excessive amount of leaves on your lawn while it is covered by mounds of snow all winter creates a chance of growing snow mold, which is a pink or gray fungal disease that can attack your grass.

You have a difficult decision. Either way, it will be important to get those leaves off as soon as possible next spring.

On another note, I'm still seeing a number of individuals advertising leaf removal. It might be worth the cost to hire someone to do this for you.

Plants that hold onto their green leaves throughout the winter are called evergreens. Those that drop their leaves are called deciduous plants. 
For example, English ivy is evergreen; Boston ivy is deciduous. 
Hope that helps.