it might. bunnies have very delicate digestive systems and any change in diet needs to be made gradually over the course of at least a couple weeks. this is esp. important with pellets, hay maybe not so much, but i would still try and get timothy hay from somewhere. another issue you might face is getting him back on the timothy. alfalfa hay tastes “better” to some bunnies than timothy, so you might be faced with a stubborn bunny when you do have timothy hay again.
alfalfa is legume hay, timothy is grass hay (some other acceptable grass hays are: orchard, oat, meadow, brome). alfalfa is higher in calories and calcium. it is recommended for baby bunnies (up to about 6 months) and in some cases for senior rabbits (6+ years) or long-haired breeds where they need extra calories. it can be used as a treat in addition to your regular timothy hay, but not as a primary hay in the case of healthy adult buns.