Adds an option "syntastic_allow_quit".

doc/syntastic.txt

@@ -208,7 +208,7 @@ errors (where possible). Highlighting can be turned off with the following >
     let g:syntastic_enable_highlighting = 0
 <
 
-                                      *'g:syntastic_always_populate_loc_list'*
+                                        *'syntastic_always_populate_loc_list'*
 Default: 0
 Enable this option to tell syntastic to always stick any detected errors into
 the loclist: >
@@ -221,6 +221,18 @@ when saving or opening a file: >
     let g:syntastic_auto_jump=1
 <
 
+                                                      *'syntastic_allow_quit'*
+Default: 1
+When the |location-list| is open and you quit a buffer, syntastic attempts to
+detect if this is the last active buffer, and quit Vim if it is.  This is
+usually what you want, but in that situation Vim will also abandon any hidden
+buffers, thus potentially destroying a carefully crafted session.  Use this
+variable to prevent syntastic from quitting Vim.
+
+When |syntastic_allow_quit| is 0 syntastic will never issue a 'quit' command: >
+    let g:syntastic_allow_quit=0
+<
+
                                                    *'syntastic_auto_loc_list'*
 Default: 2
 Use this option to tell syntastic to automatically open and/or close the

plugin/syntastic.vim

@@ -40,6 +40,10 @@ if !exists("g:syntastic_check_on_open")
     let g:syntastic_check_on_open = 0
 endif
 
+if !exists("g:syntastic_allow_quit")
+    let g:syntastic_allow_quit = 1
+endif
+
 if !exists("g:syntastic_loc_list_height")
     let g:syntastic_loc_list_height = 10
 endif

plugin/syntastic/loclist.vim

@@ -147,7 +147,9 @@ endfunction
 
 function! g:SyntasticLoclistHide()
     if len(filter( range(1, bufnr('$')), 'syntastic#util#bufIsActive(v:val)' )) == 1
+        if g:syntastic_allow_quit
             quit
+        endif
     else
         lclose
     endif