I am having the same issue.

I can see them after a restart of the game for awhile then they disappear. I have turned graphics down, updated drivers as of today. the game runs decent even on standard settings. so why is everyone disappearing? sometimes I can walk away and come back and then I can see them. others not so much.

here is the rundown on my system

OS Name Microsoft Windows 7 Home Premium
Version 6.1.7601 Service Pack 1 Build 7601
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name BRIANMATUS-HP
System Manufacturer Hewlett-Packard
System Model HP Pavilion g7 Notebook PC
System Type x64-based PC
Processor AMD A4-3300M APU with Radeon(tm) HD Graphics, 1900 Mhz, 2 Core(s), 2 Logical Processor(s)
BIOS Version/Date Hewlett-Packard F.33, 8/18/2011
SMBIOS Version 2.7
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "6.1.7601.17514"
User Name BrianMatus-HP\Brian Matus
Time Zone Eastern Standard Time
Installed Physical Memory (RAM) 8.00 GB
Total Physical Memory 7.48 GB
Available Physical Memory 5.10 GB
Total Virtual Memory 15.0 GB
Available Virtual Memory 11.8 GB
Page File Space 7.48 GB
Page File C:\pagefile.sys


Video
Name AMD Radeon HD 6480G
PNP Device ID PCI\VEN_1002&DEV_9648&SUBSYS_3568103C&REV_00\3&2411E6FE&3&08
Adapter Type ATI display adapter (0x9648), Advanced Micro Devices, Inc. compatible
Adapter Description AMD Radeon HD 6480G
Adapter RAM 512.00 MB (536,870,912 bytes)
Installed Drivers aticfx64.dll,aticfx64.dll,aticfx64.dll,aticfx32,aticfx32,aticfx32,atiumd64.dll,atidxx64.dll,atidxx64.dll,atiumdag,atidxx32,atidxx32,atiumdva,atiumd6a.cap,atitmm64.dll
Driver Version 8.930.0.0
INF File oem27.inf (ati2mtag_Sumo_Mobile section)
Color Planes Not Available
Color Table Entries 4294967296
Resolution 1600 x 900 x 60 hertz
Bits/Pixel 32
Memory Address 0xE0000000-0xF7FFFFFF
I/O Port 0x00003000-0x000030FF
Memory Address 0xF0300000-0xF033FFFF
IRQ Channel IRQ 4294967294
I/O Port 0x000003B0-0x000003BB
I/O Port 0x000003C0-0x000003DF
Memory Address 0xA0000-0xBFFFF
Driver c:\windows\system32\drivers\atikmpag.sys (8.14.1.6248, 319.50 KB (327,168 bytes), 12/5/2011 9:12 PM)

DXDiag
Operating System: Windows 7 Home Premium 64-bit (6.1, Build 7601) Service Pack 1 (7601.win7sp1_gdr.110622-1506)
Language: English (Regional Setting: English)
System Manufacturer: Hewlett-Packard
System Model: HP Pavilion g7 Notebook PC
BIOS: InsydeH2O Version CCB.03.61.22F.33
Processor: AMD A4-3300M APU with Radeon(tm) HD Graphics (2 CPUs), ~1.9GHz
Memory: 8192MB RAM
Available OS Memory: 7658MB RAM
Page File: 3295MB used, 12020MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
DxDiag Version: 6.01.7601.17514 64bit Unicode

Any information would be great. I understand that running this on a desktop would be better, but that does not solve the issue. This should be able to run the gme with next to no difficulty. and with the graphics below standard there is no reason for this issue to be happening.