Regra que permite usar um pushState nativo no htacces, onde todas as páginas irão redirecionar para index, além de declarar exceções para as pastas de css, js e imgs

.htacces

RewriteEngine On
Options +FollowSymLinks

# ----------------------------------------------------------------------
#  General Rule
# ----------------------------------------------------------------------

# Redirect all files and paths to index.html
RewriteRule ^index.html(.*)$ - [L,QSA]

# ----------------------------------------------------------------------
#  Exception to the general rule 
# ----------------------------------------------------------------------

# Declare path and files where don't apply general rules

# js/./../* -  not apply general rule redirect of all folders and files to path "/js"
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-d
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule js/(.*)$ js/$1 [L,QSA]

# img/./../* -  not apply general rule redirect of all folders and files to path "/img"
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-d
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule img/(.*)$ img/$1 [L,QSA]

# css/./../* -  not apply general rule redirect of all folders and files to path "/css"
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-d
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule css/(.*)$ css/$1 [L,QSA]

i think you can rewrite the exceptions:

# if file exists in the root-dir serve the file with the following rules instead of index.html 
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-d
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
# js/./../* -  not apply general rule redirect of all folders and files to path "/js"
RewriteRule js/(.*)$ js/$1 [L,QSA]

# img/./../* -  not apply general rule redirect of all folders and files to path "/img"
RewriteRule img/(.*)$ img/$1 [L,QSA]

# css/./../* -  not apply general rule redirect of all folders and files to path "/css"
RewriteRule css/(.*)$ css/$1 [L,QSA]