We are not aware of any viruses that affect viburnum.   Is it possible that a root rot (caused by a fungus-like organism called oomycetes) may have killed your viburnum?    Take a look at this site from the Pacific Northwest Plant Disease Management handbook - https://pnwhandbooks.org/plantdisease/host-disease/viburnum-root-rots.   Compare the described symptoms in this article with what you observed on your viburnum.   

Here is another source of information about Phytophthora root and crown rots - https://ipm.ucanr.edu/PMG/PESTNOTES/pn74133.html

Crabapple can be susceptible to Phytophthora diseases and Phytophthora can linger in the soil for a few years.   This is a list of plants know n to be susceptible -  https://horticulture.oregonstate.edu/nursery/nursery/what-phytophthora

However, the best way to minimize any potential Phytophthora or other root rot diseases is with good water management.  Poor soil drainage could also be a problem for any crabapple you plant.    You can take steps to try to improve your soil drainage by adding organic material like compost, shredded eaves.  You should use drip irrigation when watering is necessary.   You could also raise the level of the soil where you want to replant to help ensure good drainage.   

Here is some good tree planting guidance from Oregon State Extension - "Selecting, Planting, and Caring For A New Tree" https://extension.oregonstate.edu/sites/default/files/documents/ec1438.pdf