Ask Mr. Smarty Plants

We cannot tell you for sure without seeing it whether your manzanita is dead or not but there are a couple of things you can check.

Generally speaking, the fact that the leaves turned brown and brittle and did not fall off is a bad sign.  Leaf abscission is a normal process whereby a plant removes a part it no longer needs.  It physically separates the part which then falls off.  This happens annually in decidous plants and at regular intervals in evergreen ones as well.  The leaf changes color as the plant removes nutrients (and the green coloration) before separating it.  Usually if leaves turn brown and don't fall off, it means that the plant has died suddenly without performing abscission.  In situations of extreme heat or drought, a plant will often drop a number of leaves (and fruit) that it knows it doesn't have the resources to support rather than become overstressed and possibly succumb to insect damage or disease.

Time will ultimately reveal whether your plant is alive or not.  Keep it very lightly watered (it doesn't need much if it has no leaves to support).  If it has the resources to put on more leaves, the old ones will fall as the new ones emerge, but there is no reason not to remove them, if it keeps you from removing the entire plant prematurely.  You can also tell if the twigs are alive by bending them to see if they are supple.  If they are dead, they will snap off to reveal dry, brown centers.  You can also gently scrape off twig bark with a thumbnail.  If the layer below the bark is green, it is alive and the plant should bounce back.  If the ends of the twigs are dead,  prune them back a few inches at a time until you make a cut that reveals green wood at the core.  If you end up digging up the plant you can assess the roots; dead ones are black, living ones are brown with plenty of fine white hairs. 

Manzanitas Arctostaphylos manzanita (Whiteleaf manzanita) and their Texas cousin, Arbutus xalapensis (Texas madrone) madrones, are notoriously difficult to establish in a garden setting.  Like other members of the ericaceous family, they demand excellent drainage.  That is why they are often found thriving on hillsides in nature.  They are more likely to die from too much water than not enough.  After 4 years of encouraging it to grow in your garden, it will be a real disappointment to lose it so we're keeping our fingers crossed for you!