There were 2 posts from a while back that did the same thing – Erase a selected block and then heal the LINE or POLYLINE, but the annoying thing was that only one routine would work for LINES and you would need another LISP routine for it to work for polylines.

Someone asked if these could be combined into 1 LISP routine over at CADTutor.net and luckily PBE came up with the solution:

Please see the previous posts to see examples (animated gifs) of what the routine does:

https://autocadtips.wordpress.com/2012/06/29/autolisp-heal-erase-block-heal-polyline/

https://autocadtips.wordpress.com/2012/06/29/autolisp-heal-erase-block-heal-line/

Use the command EE to start

; by PBE
; http://www.cadtutor.net/forum/showthread.php?73328-Joining-2-commands
; erase a block and join the lines that the block broke
(defun c:hint ()
   (if	(setq ss (ssget '((0 . "INSERT"))))
   		(repeat (setq i (sslength ss))
		  	(setq pt  (cdr
				 (assoc  10
				   (entget
				     (setq e (ssname ss (setq i (1- i))))
				   ))))
		  	(command "_rotate" e "" "_non" pt "180")
		  )
     )(princ)
   )

(defun c:ee (/ pea $blk block i ll ur objs p1 p2)
  (vl-load-com)
  (setq pea (getvar 'Peditaccept))
  (setvar 'PeditAccept 1)
  (if (setq $blk (ssget '((0 . "insert"))))
	  (repeat (setq i (sslength $blk))
	    	(setq e (ssname  $blk (setq i (1- i))))
	  	(vla-getboundingbox (vlax-ename->vla-object e) 'll 'ur)
	    	(entdel e)
	  (setq objs (ssget "C" 
	      (setq p1 (vlax-safearray->list ll))
	      (setq p2 (vlax-safearray->list ur))
	      )
	  )
	(if (eq (cdr (assoc 0 (entget (ssname objs 0)))) "LWPOLYLINE")
		  (command "_.pedit"  "_m"  objs
			   ""  "_join" "_Joint"
			   "_Both" (distance p1 p2)
			   "" )
		  (command "_.join" (ssname objs 0) (ssname objs 1) "")
		)
	    )
    (princ "\nNo Blocks Selected")
    )
	  (setvar 'PeditAccept pea)
	  (princ)
	)