1. you can recover deleted files depending on how you deleted it and what OS/filesystem you use. for example
https://www.piriform.com/recuva
2. if you have any error dialog that pops up after starting BizHawk, post it here.
3. Since you mentioned antivirus, it could deleted .dll files from the dll directory.
Here's my dll directory list of files:
7z.dll
BizHawk.Bizware.BizwareGL.dll BizHawk.Bizware.BizwareGL.GdiPlus.dll
BizHawk.Bizware.BizwareGL.OpenTK.dll BizHawk.Bizware.BizwareGL.SlimDX.dll
BizHawk.Client.ApiHawk.dll BizHawk.Client.Common.dll
BizHawk.Common.dll BizHawk.Emulation.Common.dll
BizHawk.Emulation.Cores.dll BizHawk.Emulation.DiscSystem.dll
bizlynx.dll bizswan.dll
blip_buf.dll cgc.exe
CSharp-SQLite.dll ELFSharp.dll
ffmpeg.exe ffmpeg_readme.txt
freetype26.dll GongShell.dll
gpgx.wbx.gz ICSharpCode.SharpZipLib.dll
Ionic.Zip.dll libc.so.gz
libco.so.gz libdarm.dll
libgambatte.dll libgcc_s.so.gz
libgcc_s_seh-1.dll libpng16.dll
libquicknes.dll LibretroBridge.dll
libsnes.wbx.gz libspeexdsp.dll
libstdc++-6.dll libstdc++.so.6.gz
libvbanext.dll libwinpthread-1.dll
lua51.dll LuaInterface.dll
mgba.dll mupen64plus-audio-bkm.dll
mupen64plus-input-bkm.dll mupen64plus-rsp-hle.dll
mupen64plus-video-glide64.dll mupen64plus-video-glide64mk2.dll
mupen64plus-video-GLideN64.dll mupen64plus-video-rice.dll
mupen64plus.dll Newtonsoft.Json.dll
ngp.wbx.gz [nlua]
octoshock.dll OpenAL32.dll
OpenTK.dll OpenTK.GLControl.dll
pcfx.wbx.gz PeNet.dll
picodrive.wbx.gz sameboy.wbx.gz
SDL.dll SlimDX.dll
snes9x.wbx.gz ss.wbx.gz
System.Data.SQLite.dll uzem.wbx.gz
vb.wbx.gz Virtu.dll
wrap_oal.dll zlib1.dll
4. if you don't have any error dialogs, try (backupping, and then) deleting your config.ini file